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Early Posting

Accepted papers to appear in an upcoming issue

OSA now posts prepublication articles as soon as they are accepted and cleared for production. See the FAQ for additional information.

Detection and identification of drugs under real conditions by using a high noisy THz broadband pulse

Svetlana Varentsova and V. Trofimov

Doc ID: 268351 Received 14 Jun 2016; Accepted 24 Oct 2016; Posted 24 Oct 2016  View: PDF

Abstract: We discuss an effective method for the detection and identification of drugs using a high noisy THz signal. We add to the THz signal transmitted through a sample with illicit drug MA, a noisy THz signal obtained in real conditions. The insufficiency of the standard THz-TDS method is demonstrated because this method detects the spectral features of the neutral substances and explosives in the noisy THz signal. The discussed method is based on time-dependent integral correlation criteria calculated using spectral dynamics of medium response. We propose a new modification of the integral correlation criterion, which is less dependent on spectral characteristics of a noisy signal under investigation.

The effect of background dielectric on TE polarizedphotonic band gap of metallo-dielectric photoniccrystals using Dirichlet-to-Neumann map method

Behrooz Rezaei and Ali Asghar Sedghi

Doc ID: 272308 Received 25 Jul 2016; Accepted 24 Oct 2016; Posted 24 Oct 2016  View: PDF

Abstract: Using the Dirichlet-to-Neumann map method, we have calculated the photonic band structure of two dimensional(2D) metallo-dielectric photonic crystals having the square and triangular lattices of circular metal rods indielectric background. We have selected transverse electric (TE) mode of electromagnetic waves and the resultingband structures showed the existence of photonic band gap in these structures. We theoretically study the effect ofbackground dielectric on the photonic band gap.

Compressive spectral testbed imaging system based on thin-film color-patterned filter arrays

Hoover Rueda, Henry Fuentes, and Gonzalo Arce

Doc ID: 274070 Received 19 Aug 2016; Accepted 24 Oct 2016; Posted 24 Oct 2016  View: PDF

Abstract: Compressive spectral imaging systems have been demonstrated to be reliable in capturing multispectraldata using far fewer measurements than traditional scanning techniques. In this paper, a thin-film patternedfilter array-based compressive spectral imager is demonstrated, including its optical design andimplementation. The use of a patterned filter array entails a single-step 3D spatial-spectral coding onthe input data cube, thus providing higher flexibility on the selection of voxels being multiplexed on thesensor. The patterned filter array is designed and fabricated at micrometer pitch size thin-films, referredas pixelated filters, with three different cut-off wavelengths. The performance of the system is evaluatedin terms of references measured by a commercially available spectrometer and the visual quality of thereconstructed images. Different distributions of the pixelated filters, including random and optimizedstructures are explored.

Global calibration of unleveled theodolite using angular distance constraints

XUehan Zheng, Zhengzhong Wei, and Guangjun Zhang

Doc ID: 274080 Received 19 Aug 2016; Accepted 24 Oct 2016; Posted 24 Oct 2016  View: PDF

Abstract: Theodolite is important optical measurement instrument in application. Its global calibration, includes position and orientation, is prerequisite for measuring. Most global calibration methods require theodolite be leveled precisely, that time-consuming and susceptible. We propose a global calibration method without leveling: solves position results using angular distance of control points by nonlinear optimization, and then compute orientation parameters (rotation matrix) linearly based on position results. Furthermore, global calibration of multi-theodolite is also introduced. In addition, we introduced a method that can compute the dip direction and tilt angle by decomposing the rotation matrix. We evaluate the calibration algorithms on both computer simulation and real data experiments, demonstrating the effectiveness of the techniques.

Simultaneous measurement of refractive index distribution and topography by integrated transmission and reflection digital holographic microscopy

Jianlin Zhao, Chaojie Ma, Jianglei Di, Jiwei Zhang, Ying Li, Teli Xi, and Enpu Li

Doc ID: 274359 Received 23 Aug 2016; Accepted 24 Oct 2016; Posted 24 Oct 2016  View: PDF

Abstract: We propose a method for simultaneously measuring dynamic changes of the refractive index distribution and surface topography, which integrates the transmission and reflection digital holographic microscopy based on polarization and angular multiplexing techniques. The complex amplitudes of the transmitted and reflected object waves can be simultaneously retrieved. The phase information of the reflected object wave is directly used to determine the topography of the specimen which corresponds to its physical thickness. Assuming that the refractive index distribution is uniform in the direction of the specimen thickness, the refractive index distribution can be deduced from the phase distributions of the transmitted and reflected object waves without any approximation. The refractive index distribution and dynamic changes of the topography of a tiny deionized water droplet have been measured for the availability of the proposed method.

Optical coherence tomography imaging of capillary reperfusion after ischemic stroke

Jonghwan Lee, Buyin Fu, Yasemin Gursoy-Ozdemir, David Boas, and Turgay Dalkara

Doc ID: 275096 Received 02 Sep 2016; Accepted 23 Oct 2016; Posted 24 Oct 2016  View: PDF

Abstract: Although progress has been made for recanalization therapies after ischemic stroke, post-treatment imaging studies show that tissue reperfusion cannot be attained despite satisfactory recanalization in a significant percentage of patients. Hence, investigation of microcirculatory changes in both surface and deep cortical levels after ischemia-reperfusion is important for understanding the post-stroke blood flow dynamics. In this study, we applied optical coherence tomography (OCT) imaging of cerebral blood flow for the quantification of the microcirculatory changes. We obtained OCT microangiogram of the brain cortex in a mouse stroke model and analyzed the data to trace changes in the capillary perfusion level (CPL) before, during, and after the stroke. The CPL changes were estimated in one- and two-hour ischemia groups as well as in non-ischemic sham-operated group. For the estimation of CPL, a decorrelation amplitude-based algorithm was implemented and used. As a result, the CPL considerably decreased during ischemia but recovered to the baseline when recanalization was performed 1-hour after ischemia; however, the CPL was significantly reduced when recanalization was delayed to 2-hours after ischemia. These data demonstrate that ischemia causes microcirculation dysfunction, leading to a decreased capillary reperfusion after recanalization. Microcirculatory no-reflow warrants more rigorous assessment in clinical trials, whereas advanced optical imaging techniques may provide mechanistic insight and solutions in experimental studies.

Sizing submicron particles from optical scattering data collected with oblique incidence illumination

Ran Liao, Paul Roberts, and Jules Jaffe

Doc ID: 274262 Received 26 Aug 2016; Accepted 22 Oct 2016; Posted 24 Oct 2016  View: PDF

Abstract: As submicron particles play an important role in a variety of ecosystems that include aqueous, terrestrial and atmospheric, a measurement system to quantify them is highly desirable. In pursuit of formulating and fabricating a system to size them using visible light, a system that collects multi-directional scattered light from individual particles is proposed. A prototype of the system was simulated, built, and tested via calibration with a set of polystyrene spheres in water with known sizes. Results indicate that the system is capable of accurately resolving the size of these particles in the 0.1 to 0.8 μm range. The system incorporates a novel design that uses oblique illumination to collect scattered light over a large range of both forward and backward scatter angles. This is then followed by the calculation of a ratio of forward to backscattered light, integrated over a suitably defined range. The monotonic dependence of this ratio upon particle size, leads to an accurate estimate of particle size. The method was explored first, using simulations, then followed with a working version. The sensitivity of the method to a range of relative refractive index was tested using simulations. The results indicate that the technique is relatively insensitive to this parameter and thus of potential use in the analysis of particles from a variety of ecosystems. The article concludes with a discussion of a variety of pragmatic issues, including the required dynamic range as well as further research needed with environmentally relevant specimens to create a pragmatic instrument.

Non-linear laser dynamics induced by frequency shifted optical feedback: Application to vibration measurements

eric lacot, Vadim GIRARDEAU, Carolina GOLONI, Olivier Jacquin, olivier HUGON, and Mehdi INGLEBERT

Doc ID: 276535 Received 23 Sep 2016; Accepted 22 Oct 2016; Posted 24 Oct 2016  View: PDF

Abstract: In this article, we study the non-linear dynamics of a laser subjected to frequency shifted optical reinjection coming back from a vibrating target. More specifically, we study the non-linear dynamical coupling between the carrier and the vibration signal. The present work shows how the non-linear amplification of the vibration spectrum is related to the strength of the carrier and how it must be compensated to obtain accurate (i.e. without bias) vibration measurements. The theoretical predictions, confirmed by numerical simulations, are in good agreement with the experimental data. The main motivation of this study is the understanding of the non-linear response of a LOFI (Laser Optical Feedback Imaging) sensor for quantitative phase measurements of small vibrations, in the case of strong optical feedback.

Measurement of the reflection and loss of the hybridair-core photonic-bandgap fiber ring resonator

Hanzhao Li, Jianjie Zhang, Linglan Wang, Huilian Ma, and Zhonghe Jin

Doc ID: 275843 Received 19 Sep 2016; Accepted 21 Oct 2016; Posted 21 Oct 2016  View: PDF

Abstract: A fiber ring resonator is the key element in a resonant fiber optic gyroscope (RFOG). Both reflection and loss characteristics can severely decrease the accuracy of the RFOG. This paper firstly implements the optical frequency domain reflectometry (OFDR) to measure the reflection and loss coefficients of the hybrid air-core photonic bandgap fiber (PBF) ring resonator. Compared with the traditional measurement method of the resonant curve, the OFDR can clearly distinguish the two junctions between the air-core PBF and the solid-core fiber. The measured reflection coefficients at the two splicing points are 1.77% and 2.65%, respectively. The excess losses are 2.28 dB and 3.22 dB, respectively. Thus the measurement of the junctions in the fiber ring resonator is realized.

Diffractive Array Optics tuned by Rotation

Adrian Grewe, Stefan Sinzinger, and Patrick Feßer

Doc ID: 272986 Received 02 Aug 2016; Accepted 21 Oct 2016; Posted 24 Oct 2016  View: PDF

Abstract: In this work we apply the Alvarez-Lohmann principle for varifocal lenses to diffractive off axis elements tuned by rotation. Two methods to combine multiple elements into arrays are presented. Further we show that inverse phase sections result from a 2π ambiguity of the rotation. Quantization techniques are applied to eliminate these unwanted sections. As proof of concept a retro focus lens using a tuneable diffractive lens array is presented.

Dispersive mirror for the mid-infrared spectral range of 9 to 11.5 µm

Florian Habel and Vladimir Pervak

Doc ID: 273251 Received 30 Aug 2016; Accepted 21 Oct 2016; Posted 24 Oct 2016  View: PDF

Abstract: A dispersive multilayer interference mirror with a group delay dispersion (GDD) of +1500 fs² for the spectral range of 9 to 11.5 µm is presented. It is designed to compensate the GDD of a ultrashort light pulse gained when transmitting 1 mm of a zinc selenide substrate. The coating process for the mirror manufacturing is described. The optical properties of the mirror are fully characterized by measuring the group delay (GD), the GDD, the reflectance and the transmittance.

Fabrication of short-wavelength infrared dual-band-pass filter based on combination of Fabry-Perot filters

Yuan Cai, Zhou Sheng, Xiaofeng Ma, and Dingquan Liu

Doc ID: 276340 Received 23 Sep 2016; Accepted 21 Oct 2016; Posted 24 Oct 2016  View: PDF

Abstract: Dual-band-pass filters are key optical components in dual-spectral detection applications, it is imperative to fabricate them in a relatively simple way for practical use. In this paper, a dual-band-pass filter working in short-wavelength infrared is developed by combination of two Fabri-Perot filters each having a transparent band. These two filters are designed separately, and deposited at the different side of a substrate. The total layers’ number of the dual-band-pass filter is limited to 36, these layers are monitored by the method of direct transmittance level cut monitoring with a single monitor wavelength. The percent of optical extremums monitoring strategy is adopted in the deposition. The spectrums of the F-P filters and the dual-band-pass filter are tested. The shorter pass-band’s average transmittance is above 84%, the longer one is above 88%, and four of the pass-bands’ edge steepness values are 1.4%, 2.8%, 1.9%, 1.7%.

Effects of Particle Locations on Reconstructed Particle Images in Digital Holography

Christina Hesseling, Tim Homeyer, Joachim Peinke, and Gerd Gülker

Doc ID: 274377 Received 23 Aug 2016; Accepted 21 Oct 2016; Posted 24 Oct 2016  View: PDF

Abstract: The intensity and phase reconstructed from digital in-line holograms by the convolution approach are analysed. Distortions of particle images depending on their position in the plane transverse to the optical axis are identified. For this purpose, the object fields of numerically simulated particle holograms as well as of experimental data are reconstructed. The results of three dimensional correlations of numerical and experimental data yield superior results when the numerically generated reference volumes are adapted to the transverse locations of the particle. Thus, proof is given that the characteristics of a particle image change distinctly with the transverse position of the particle and that the numerical model successfully simulates these changes. Hence, this knowledge can be integrated in future particle position detection algorithms.

Endlessly single-mode photonic crystal fiber as a high resolution probe

Heli Lukner, Peeter Piksarv, Sandhra-Mirella Valdma, and Jaagup Repän

Doc ID: 274527 Received 26 Aug 2016; Accepted 21 Oct 2016; Posted 24 Oct 2016  View: PDF

Abstract: We sample ultrabroadband light, focused to a diffraction limited spot, to an endlessly single mode photonic crystal fiber (ESM), and detect both the field amplitude and phase using a SEA TADPOLE interferometer. We resolve spatial features up to 2.5 times finer than the fiber mode size while sampling the periodic features of bipolar oscillating field in transverse section. The resolution enhancement is expected also in other types of single mode fibers in intensity measurement and leads to an inexpensive method for characterizing point spread function of such optical fields, e. g., diffraction limited spots from microscope objectives. In addition, we demonstrate guidance of high NA light field in the fine structure of ESM fiber mode. The results are especially valuable for the devices where a fiber tip acts as an input slit and defines the spatial resolution, e. g., fiber-based interferometers, spectrometers, and sensors.

Acceleration of hologram generation by optimizing the arrangement of wavefront recording planes

Naotaka Hasegawa, Tomoyoshi Shimobaba, Takashi Kakue, and Tomoyoshi Ito

Doc ID: 272113 Received 21 Jul 2016; Accepted 21 Oct 2016; Posted 24 Oct 2016  View: PDF

Abstract: For a three-dimensional display using computer-generated holograms (CGHs), fast CGH calculations are required. The multiple wavefront recording planes (WRPs) method can reduce the computational amount by placing WRPs near an object. In previous studies using this method, the numbers and intervals of the WRPs were fixed. Hence, the calculation time was heavily affected by calculation conditions such as variation in the distribution of object points. This paper proposes a method that can automatically optimize the number and arrangement of WRPs to accelerate CGH generation.

Automated Assessment and Tracking of Human Body Thermal variations using unsupervised clustering

Bardia Yousefi, Julien Fleuret, Hai Zhang, Xavier Maldague, RAYMOND WATT, and MATTHIEU KLEIN

Doc ID: 271996 Received 21 Jul 2016; Accepted 21 Oct 2016; Posted 21 Oct 2016  View: PDF

Abstract: The presented approach addresses a review on the overheating which occurs during radiological examinations such as MRI and a series of thermal experiments to determine the thermal suitable fabric material which should be used for radiological gowns. Moreover, an automatic system for detecting and tracking of the thermal fluctuation is presented. It applies HSV based kernelled k-means clustering which initializes and controls the points which lie on the Region of Interest (ROI) boundary. Afterwards a particle filter tracks the targeted ROI during the video sequence independent to previous locations of the overheating spots. The proposed approach was tested during some experiments and under conditions very similar to those used during real radiology exams. Six subjects have voluntarily participated in these experiments. To simulate the hot spots occurring during the radiology, a controllable heat source was utilized near the subject’s body. The results indicate promising accuracy for the proposed approach to track the hot spots. Some approximations were used regarding the transmittance of the atmosphere and emissivity of the fabric could be neglected because of the independency of the proposed approach for these parameters. The approach can track the heating spots continuously and correctly, even for moving subjects, and provides considerable robustness against motion artifact, which usually occurs during most medical radiology procedures.

Low-cost encoder using a phase shifting algorithm with polarization properties of light

Sergio Alvarez-Rodríguez and Noe Alcalá Ochoa

Doc ID: 273776 Received 12 Aug 2016; Accepted 20 Oct 2016; Posted 21 Oct 2016  View: PDF

Abstract: In this work a novel polyphase optical encoder is presented, which uses a mathematical algorithm designed to take advantage of the polarization properties of the light. This optical encoder is endowed with excellent capabilities of accuracy, precision and resolution in measuring the angle position for a shaft. As it is designed with low-cost optical components, expensive components are not required at all. At first, a light beam passes through a rotating polarizer, and actual readings are obtained from low-cost photoresistors located under phase-shifted analyzers to generate characteristic curves for each of the phases, in the plane formed by the measured angle and the intensity of light. These curves are correlated to the ideal polarization curve formed by the Malus’ law, via polynomial expressions, in order to obtain the relationship between actual values and the ideal square cosine. After this characterization process, the encoder isready to be used indefinitely, and operational data are introduced to a Phase Shifting algorithm in order to obtain, on-line, the angle position of any rotating device.

Calibration of oblique-incidence reflectivity difference (OI-RD) for label-free detection of molecular layer

Yiyan Fei, Chenggang Zhu, Ru Chen, Yuzhangyang Zhu, Xu Wang, Xiangdong Zhu, Lan Mi, and Fengyun Zheng

Doc ID: 270382 Received 24 Aug 2016; Accepted 20 Oct 2016; Posted 20 Oct 2016  View: PDF

Abstract: Oblique-incidence reflectivity difference (OI-RD) is a form of polarization-modulation ellipsometry that measures properties of thin films on a solid surface through the change in polarization state of light upon reflection from the surface. The measurement accuracy depends on precisions of the phase modulation amplitude and azimuthal alignments of key polarizing optical elements and thus requires careful calibration. In present work, we describe robust methods of such calibration that enable precise determination of the modulation amplitude and static retardation of a phase modulator and azimuths of key polarizing optics in an OI-RD system.

PMT Calibration Based on Na Lidar Observation and Its Effect on Heat Flux Bias

Alan Liu and Yafang Guo

Doc ID: 274085 Received 19 Aug 2016; Accepted 19 Oct 2016; Posted 20 Oct 2016  View: PDF

Abstract: Na lidar can measure vertical wind and temperature at high temporal and vertical resolutions, enough to resolve gravity wave perturbations. Heat flux due to dissipating gravity waves is an important quantity that can be derived from such perturbations. When the lidar signals are high, a photomultiplier tube (PMT) used to count incoming photons may suffer from saturation effect and its output count is not linearly related to incoming photon counts. Corrections to this effect can be measured in a laboratory setting but may have large errors at high count rates. We show that the errors in the PMT correction can cause significant bias in the heat flux calculation due to the inherent correlation between wind and temperature errors. Using the measurements made by the Na Lidar at the Andes Lidar Observatory with Hamamatsu PMTs, we developed a calibration procedure to remove such PMT correction errors from laboratory measurements. By applying the revised PMT correction curve we demonstrated that the heat flux bias can be removed through this procedure.

Angular velocity estimation based on star vector with improved current statistical model Kalman filter

Lu Jiazhen, Zhang Hao, Yanxiong Niu, and zhang he

Doc ID: 274489 Received 26 Aug 2016; Accepted 19 Oct 2016; Posted 20 Oct 2016  View: PDF

Abstract: Angular velocity information is a requisite for spacecraft guidance, navigation and control system. In this paper, a novel approach for angular velocity estimation merely based on star vectors measurement with improved current statistical model Kalman filter(ICSMKF) is proposed. High precision angular velocity estimation can be achieved under dynamic conditions. The amount of calculation is also reduced compared with Kalman filter. Different trajectories are simulated to test this approach and experiments with real starry sky observation are implemented for further confirmation. The estimation accuracy is proved to be better than 10-4 rad/s under various conditions. Both simulation and experiment demonstrate that the described approach is effective and shows an excellent performance under both static and dynamic conditions.

Single-step fabrication of thin-film linear variable bandpass filters based on metal-insulator-metal geometry

Calum Williams, Girish Rughoobur, Andrew Flewitt, and Timothy Wilkinson

Doc ID: 275019 Received 06 Sep 2016; Accepted 19 Oct 2016; Posted 19 Oct 2016  View: PDF

Abstract: A single-step fabrication method is presented for ultra-thin, linearly variable optical bandpass filters (LVBFs) based on a metal-insulator-metal arrangement using modified evaporation deposition techniques. This alternate process methodology offers reduced complexity and cost in comparison to conventional techniques for fabricating LVBFs. We are able to achieve linear variation of insulator thickness across a sample, by adjusting the geometrical parameters of a typical physical vapor deposition process. We demonstrate LVBFs with spectral selectivity from 400 - 850 nm based on Ag (25 nm) and MgF2 (75 - 250 nm). Maximum spectral transmittance is measured at ~70% with a Q-factor of ~20.

Wide-bandgap nonlinear crystal LiGaS₂ for femtosecond mid-infrared spectroscopy with chirped-pulse upconversion

Ryosuke Nakamura, Yoshizumi Inagaki, Hidefumi Hata, Norio Hamada, Nobuhiro Umemura, and Tomosumi Kamimura

Doc ID: 275174 Received 07 Sep 2016; Accepted 19 Oct 2016; Posted 19 Oct 2016  View: PDF

Abstract: Femtosecond time-resolved mid-infrared (MIR) spectroscopy based on the chirped-pulse upconversion is a promising method for observing molecular vibrational dynamics. A quantitative study on nonlinear media for the upconversion is still essential for its wide applications particularly at the frequencies below 2000 cm-1. We evaluate wide-bandgap nonlinear crystals of Li-containing ternary chalcogenides on their performance as the upconversion medium for femtosecond MIR spectroscopy. The upconversion efficiency is measured as a function of the MIR pulse frequency and the chirped pulse energy. LiGaS₂ is found to be an efficient crystal for the upconversion of MIR pulses in a wide frequency range of 1100–2700 cm-1, especially below 2000 cm-1. By using LiGaS₂ as an efficient upconversion crystal, we develop a MIR pump-probe spectroscopy system with a spectral resolution of 2.5 cm-1 and a time resolution of 0.2 ps. Vibrational relaxation dynamics of CO stretching modes of Mn₂(CO)₁₀ in cyclohexane and bovine serum albumin in D₂O are demonstrated with a high signal-to-noise ratio.

Polarized Transfer Functions of the Ocean Surface for Above-Surface Determination of the Vector Submarine Light Field

Robert Foster and Alexander Gilerson

Doc ID: 270136 Received 12 Jul 2016; Accepted 19 Oct 2016; Posted 20 Oct 2016  View: PDF

Abstract: A method is developed to determine the underwater polarized light field from above sea surface observations. A hybrid approach combining vector radiative transfer simulations and the Monte Carlo method is used to determine the transfer functions of polarized light for wind-driven ocean surfaces. Transfer functions for surface-reflected skylight and upward transmission of light through the sea surface are presented for many common viewing and solar geometries. Sensitivity of reflection matrices to environmental conditions is examined and can vary up to 50% due to wind speed, 25% due to atmospheric aerosol load, and 10% due to radiometer field-of-view. Scalar transmission is largely independent of water type and varies a few percent with wind speed, while polarized components can change up to 10% in high winds. Considerations for determining the water-leaving radiance (scalar or vector) are discussed.

Modelling and Validation of Uniform Large AreaOptical Coating Deposition on a Rotating Drum UsingMicrowave Plasma Reactive Sputtering

Des Gibson, CHENG LI, Shigeng Song, david child, Hin On Chu, and Ewan Waddell

Doc ID: 274929 Received 30 Aug 2016; Accepted 18 Oct 2016; Posted 18 Oct 2016  View: PDF

Abstract: Magnetron sputter deposition onto a rotating drum is a method applied to high throughput large area optical coating deposition,where film physical thickness uniformity is an important parameter. Techniques have been developed such asmasking/substrate movement, in order to improve sputtered film uniformity. In this study, a model is described and validatedfor predicting film uniformity. Experimental data shows excellent agreement with modelled simulations, with and without amodified sputtering mask. Practical application is demonstrated in maximising uniformity over an individual substrate size of100 cm2 for a high optical density visible/near infrared dual band laser protection filter.

Generation of High-Contrast and High-Spatial QualityIdler from A Low-Gain Optical Parametric Amplifier

Ahmed Sharba, Gagik Nersisyan, Mathew Zepf, Nicholas Stuart, Roland Smith, Marco Borghesi, and Gianluca Sarri

Doc ID: 274948 Received 30 Aug 2016; Accepted 18 Oct 2016; Posted 18 Oct 2016  View: PDF

Abstract: The temporal contrast of a regeneratively amplified, sub-picosecond pulse is enhanced employing a low-gain optical parametric amplification stage self-pumped by the second-harmonic of the pulse. Through careful characterization of the two related non-linear processes and optimization of the non-collinear geometry, a robust high-contrast idler pulse has been generated, with excellent spatial quality in both the near and far field. The overall energy conversion efficiency exceeds 14%, with 33% intensity conversion efficiency. The temporal cleaning is implemented without any bandwidth losses or spectral shift and produces approximately 20% temporal shortening. These experimental findings are in excellent agreement with numerical calculations.

Black Phosphorus based One-dimensional Photonic Crystals and Microcavities

Francesco Scotognella, Ilka Kriegel, and Stefano Toffanin

Doc ID: 276454 Received 23 Sep 2016; Accepted 18 Oct 2016; Posted 18 Oct 2016  View: PDF

Abstract: The latest achievements in the fabrication of black phosphorus thin layers, towards the technological breakthrough of a phosphorene atomically thin layer, are paving the way for their employment in electronics, optics, and optoelectronics. In this work, we have simulated the optical properties of one-dimensional photonic structures, i.e. photonic crystals and microcavities, in which few-layer black phosphorus is one of the components. The insertion of the 5 nm black phosphorous layers leads to a photonic band gap in the photonic crystals and a cavity mode in the microcavity interesting for light manipulation and emission enhancement.

Developing a trend prediction model of subsurfacedamage for fixed-abrasive grinding of optics by cupwheels

Haobo cheng and Zhichao Dong

Doc ID: 270404 Received 12 Jul 2016; Accepted 18 Oct 2016; Posted 19 Oct 2016  View: PDF

Abstract: Fixed-abrasive grinding by cup-wheels plays an important role in the production of precision optics. During cupwheelgrinding, what we exactly want are large removal rate while maintaining a fine integrity in both surface andsubsurface layer (academically recognized as surface roughness and subsurface damage, respectively). This studydevelops a theoretical model used to predict the trend of subsurface damage of optics (with respect to variousgrinding parameters) in fixed-abrasive grinding by cup-wheels. It is derived from the maximum undeformed chipthickness model, and it successfully correlates the pivotal parameters of cup-wheel grinding with the subsurfacedamage depth. The efficiency of this model is then demonstrated by a set of experiments performed on a cup-wheelgrinding machine. In these experiments, the characteristics of subsurface damage are inspected by a wedgepolishingplus microscopic inspection method, revealing that the subsurface damage induced in cup-wheel grindingis composed of craterlike morphologies and slender cracks, with depth ranging from ~6.2μm to ~13.2μm underthe specified grinding parameters. With the help of the proposed model, an optimized grinding strategy is suggestedfor realizing fine subsurface integrity, as well as high removal rate, which can alleviate the workload of subsequentlapping and polishing.

Tunable mode rotator for space division multiplexingbased on few mode-polarization maintaining fiber

Xiaobin Hong, Xinglin Zeng, Yan Li, Qi Mo, Yongjie Tian, Wei Li, Zhijian Liu, and Jian Wu

Doc ID: 273347 Received 08 Aug 2016; Accepted 18 Oct 2016; Posted 19 Oct 2016  View: PDF

Abstract: In this paper, a fiber based tunable mode rotator is proposed and demonstrated by using the few mode-polarization maintaining fiber (FM-PMF). The mode birefringence in FM-PMF causes phase difference between two orthogonal degenerate modes, and with variation of the aligning angle between injected LP11 (LP21) mode axis and FM-PMF axis the intended another LP11 (LP21) mode with a certain orientation is generated at the FM-PMF output.

Practical automated glass selection and the design of apochromats with large field of view

Ronian Siew

Doc ID: 274114 Received 25 Aug 2016; Accepted 18 Oct 2016; Posted 19 Oct 2016  View: PDF

Abstract: This engineering note presents an automated approach to the selection of optical glasses for the design of an apochromatic lens with large field of view, based on a design originally provided by Yang et al. [A. Yang, X. Gao, and M. Li, App. Opt. 55, 5977 – 5985 (2016)]. Following from the above reference’s preliminary optimized structure, it is shown that the effort of glass selection is significantly reduced by using the global optimization feature in the Zemax optical design program. The glass selection process is very fast, within minutes, and the key lies in automating the substitution of glasses found from the global search without the need to simultaneously optimize any other lens parameter during the glass search. The result is an alternate optimized version of the lens from the above reference possessing zero axial secondary color within the visible spectrum, and a large field of view. Supplementary material is provided in the form of Zemax and text files, before and after final optimization.

Variable diameter CO2 laser ring-cutting system adapted to a zoom microscope for applications on polymer tapes

Erik Förster, Patrick Bohnert, Matthias Kraus, Roland Kilper, Ute Mueller, Martin Buchmann, and Robert Brunner

Doc ID: 274893 Received 30 Aug 2016; Accepted 18 Oct 2016; Posted 19 Oct 2016  View: PDF

Abstract: This paper presents the conception and implementation of a variable diameter ring-cutting system for a CO2 laser with a working wavelength of 10.6 µm. The laser cutting system is adapted to an observation zoom microscope for combined use and is applicable for the extraction of small circular areas from polymer films such as forensic adhesive tapes in a single shot. The variable diameter ring-cutting system provides telecentricity in the target area. Ring diameters are continuously tuneable between 500 µm and 2 mm. A minimum width of less than 20 µm was found for the ring profile edge. The basic characteristics of the system were experimentally evaluated and demonstrated by cutting experiments on different polymer tapes and further exemplary samples.

Time-resolved imaging and optical spectroscopy of plasma plumes during pulsed laser materialdeposition

Rosario Sausa

Doc ID: 270902 Received 19 Jul 2016; Accepted 18 Oct 2016; Posted 21 Oct 2016  View: PDF

Abstract: We employ fast imaging photography and emission spectroscopy to study plasma plumesresulting from the 248-nm ablation of barium strontium titanate, and utilize x-ray diffractionanalysis and scanning electron microscopy to characterize the deposited thin films.Hydrodynamic plume analyses yield initial velocities of ~ 20 km/s and spectral simulationsof the Ba I lines between 739 and 770 nm yield temperatures of ~17000 K at early times invacuum. Analyses of the Stark broadened Ba II linewidths at 614 and 649 nm reveal anelectron number density of ~10+18 cm-3 near the surface. Several Pa of oxygen reduces thesevalues, while improving the film quality.

Normal-incidence reflectance difference spectroscopy based on a liquid crystal variable retarder

Shuchun HUO, Chunguang Hu, Wanfu Shen, yanning li, lidong sun, and Xiaotang Hu

Doc ID: 270598 Received 15 Jul 2016; Accepted 18 Oct 2016; Posted 18 Oct 2016  View: PDF

Abstract: We proposed a liquid crystal variable retarder based reflectance difference spectroscopy for the normal-incidence measurements. Principles, instrumentation, data collection and reduction, and calibration procedure are provided. The signal noise is better than 0.1% and the spectral range is from 1.6eV to 2.4eV with 346 photon energy channels. As a demonstration, reflectance difference signals of a multilayer Pentacene film on poly (ethylene terephthalate) (PET) film are presented with different polarization azimuths. The characteristic peaks at 1.8eV and 1.97eV, corresponding to the Davydov splitting of Pentacene crystal, are observed which indicate well-ordered in-plane anisotropic structure of Pentacene crystal film on PET. Thanks to normal incidence this design is immune to adjust the optical structure for the measurements with different working distances and the objective lens is easily integrated to realize micro area measurement.

A holographic waveguide display with a combined-grating as an in-coupler

Jingjing Guo, yan tu, Lanlan Yang, Lili Wang, and bao wang

Doc ID: 270869 Received 20 Jul 2016; Accepted 18 Oct 2016; Posted 18 Oct 2016  View: PDF

Abstract: Volume holographic gratings are widely used as couplers in eyewear waveguide display systems but they show arelative lower TM polarized energy compared to TE incidence. In this paper, we propose a novel holographicwaveguide display system with a combined-grating as the in-coupler. When used as an in-coupler for a holographicwaveguide display system, a subwavelength metal grating is designed onto the volume holographic grating toincrease the total diffraction efficiency of the coupling gratings. Theoretical calculations show that this designincreases the diffraction efficiency by 16.4% for TM polarization, 4.3% for TE mode and 10.0% for unpolarizedlight, compared to a single volume holographic grating. Calculations also show that the use of this design as an incouplerfor a holographic waveguide system increases the luminance efficiency for these three modes by 26.8%,9.0% and 15.6%, respectively.

Ultra-flat Supercontinuum Generated from High Power, Picosecond Telecommunication Fiber Laser Source

Ruoyu Liao, Youjian Song, Xiaokang Zhou, Lu Chai, Qingyue Wang, and Ming-lie Hu

Doc ID: 273649 Received 12 Aug 2016; Accepted 18 Oct 2016; Posted 18 Oct 2016  View: PDF

Abstract: An ultra-flat high power supercontinuum generated from picosecond telecommunication fiber laser was presented. Pulse from a carbon nanotube (CNT) mode-locked oscillator was amplified using an Er-Yb-codoped fiber amplifier. The output of the system achieved an average power of 2.7 W, with the center wavelength at 1564 nm, full-width-half-maximum (FWHM) 6 nm in spectral domain. Passing this amplified high-power pulse through a 5 m high-nonlinear photonic crystal fiber (PCF), an ultra-flat supercontinuum spanning from 1600 to 2180 nm with 1 dB uniformity is generated. And the average power of the supercontinuum achieves 1 W.

A Matter of Style: Adolf Lohmann’s Approach toOptical Phase Space

Markus Testorf

Doc ID: 274369 Received 23 Aug 2016; Accepted 18 Oct 2016; Posted 18 Oct 2016  View: PDF

Abstract: Phase space optics was one of Adolf Lohmann’s favorite research topics and appears frequently in hiswork. With a unique style he applied the phase-space perspective to a variety of optical problems, witha focus on more comprehensible problem solutions and a particular interest to analyze optical signalsand systems in terms of their space-bandwidth product requirements. In his work, optical phase spaceis promoted as a hybrid of paraxial wave optics and geometrical optics. In contrast to more rigorousnotions of phase space, Adolf Lohmann preferred a heuristic approach which avoids almost entirely themathematical formalism associated with the Wigner distribution function. This approach is introducedfor the first time as a distinct way to apply phase-space optics. The application of Adolf Lohmann’s phasespaceoptics to paraxial optical cloaking, the Lohmann-Alvarez lens, and holography is not only used toexemplify this unique form of phase-space optics, but also to highlight Adolf Lohmann’s unique andcreative way of problem solving.

Measurement of Airy-vortex beam’s topologicalcharges based on pixelated micropolarizer array

Qingchuan Zhang, Zhang Yuntian, Xuan Ma, Zhaoxiang Jiang, Tan Xu, Xiao-ping WU, and Shangquan Wu

Doc ID: 274545 Received 26 Aug 2016; Accepted 17 Oct 2016; Posted 18 Oct 2016  View: PDF

Abstract: In this paper, we numerically studied the intensity patterns and screw phases of embedded optical vortex in Airybeam generated by a 3/2 phase patterns imposed on SLM. It is found that the relative position between opticalvortex and Airy beam’s mainlobe are going close during the propagation, which means the energy of Airy beam’sintensity peaks can be taken advantage by the imposed vortice. Based on pixelated micropolarizer array (PMA) inthe interference path, we succeeded to measure the integer topological charges up to -10 according to the phasejump. Besides that, fractional topological charges were also obtained in the experiment. Both of the experimentalresults are acquired in a high-precision and robust way. This work will promote potential application of Airyvortexbeam (AiVB) in fields like optical manipulation, laser proceessing, photon entanglement and the like.

Coherent superresolution imaging via grating-based illumination

Jeff Wilde, Joseph Goodman, Yonina Eldar, and Yuzuru Takashima

Doc ID: 270944 Received 20 Jul 2016; Accepted 17 Oct 2016; Posted 18 Oct 2016  View: PDF

Abstract: We describe two superresolution coherent imaging techniques, both utilizing a diffraction grating to direct high spatial frequency information, that would otherwise be lost, through the imaging system pupil. The resulting optical field in the image plane is detected by means of digital holography. Multiple measurements are taken with the illumination condition altered between exposures. In one case, linear signal processing is used to separate aliased spectral regions. In the second case the spectral regions are directly measured. In both cases, a higher-bandwidth synthetic aperture spectrum is stitched together and used to reconstruct superresolution images. Experimental results validate the approaches, demonstrating a resolution gain factor of approximately 2.5.

Analytical and Simulation Results of Triple Micro WGM ProbeSystem for 3D Blood Flow Rate Sensor

Preecha Yupapin, Surasak Chiangga, and Prateep Phatharacorn

Doc ID: 272288 Received 26 Jul 2016; Accepted 17 Oct 2016; Posted 18 Oct 2016  View: PDF

Abstract: The whispering gallery mode (WGM) is generated by light propagating within a nonlinear micro-ring resonator, whichis modeled and made by an InGaAsP/InP material, called a Panda ring resonator. An imaging probe can also be formedby the micro-conjugate mirror function the appropriate Panda ring parameter control. The 3D WGM probe can begenerated and used for 3D sensor head and imaging probe. The analytical details and simulation results are given, inwhich the simulation results are obtained by using the MATLAB and Opti-wave prop\grams. From the obtained results,such a design system can be configured to be a thin film sensor system that can contact on the sample surface for therequired measurements The outputs of the system are in the form of WGM beam, where the 3D WGM probe is alsoavailable with the micro-conjugate mirror function. Such a 3D probe can penetrate into the blood vessel and content,from which the time delay among those probes can be detected and measured, where finally, the blood flow rate can becalculated, the blood content 3D image can also be seen, which can be used for medical diagnosis purpose. The testedresults have shown that the blood flow rate of 0.72-1.11 μs-1, with the blood density of 1,060 kgm-3 can be obtained.

Optics research at the U.S. Army Research Laboratory

K. Choi, Joseph Mait, John Pellegrino, and Gary Wood

Doc ID: 273010 Received 05 Aug 2016; Accepted 17 Oct 2016; Posted 18 Oct 2016  View: PDF

Abstract: The U.S. Army Research Laboratory (ARL) is the Army's premier laboratory for land forces. The Army relies on ARLfor scientific discoveries, technological advances, and analyses that enable capabilities a future Army will need topersevere over adversaries. Although a relatively young organization that will celebrate 25 years of the discovery,innovation, and transition of science and technology in October 2017, ARL has already had significant impact in awide range of scientific and technological disciplines. In this article, we highlight some of its past and recentachievements in optics and photonics.

A 1.6 kW Yb fiber amplifier using chirped seed amplification for SBS suppression

Jeffrey White, Mark Harfouche, John Edgecumbe, Naresh Satyan, George Rakuljic, Vijaysekhar Jayaraman, Christopher Burgner, and Amnon Yariv

Doc ID: 273015 Received 02 Aug 2016; Accepted 17 Oct 2016; Posted 18 Oct 2016  View: PDF

Abstract: In a high power fiber amplifier, a frequency-chirped seed interrupts the coherent interaction between the laser and Stokes waves, raising the threshold for stimulated Brillouin scattering. Moving the external mirror of a vertical cavity surface-emitting diode laser 0.2 µm in 10 µs can yield a frequency chirp of 5×1017 Hz/s at a nearly constant output power. Opto-electronic feedback loops can linearize the chirp, and stabilize the output power. The simple and deterministic variation of phase with time preserves temporal coherence, in the sense that it is straightforward to coherently combine multiple amplifiers despite a large path length mismatch. The seed bandwidth, as seen by the counter-propagating SBS, also increases linearly with fiber length, resulting in a nearly-length-independent SBS threshold. Experimental results at the 1.6 kW level with a 19 m delivery fiber will be presented. A numerical simulation will also be presented.

Efficient Generation of 1.9 W yellow light by Cascaded Frequency Doubling of a DBR Tapered Diode

Mathias Christensen, Anders Hansen, Danny Noordegraaf, Peter Heist, Evangelos Papastathopoulos, Valentin Loyo-Maldonado, Ole Jensen, and Peter Skovgaard

Doc ID: 273770 Received 12 Aug 2016; Accepted 17 Oct 2016; Posted 17 Oct 2016  View: PDF

Abstract: We demonstrate a compact and robust diode based laser system in the yellow spectral range. The system generates 1.9 W of single frequency light at 562 nm, by cascaded single pass frequency doubling of an 1125 nm distributed Bragg reflector (DBR) tapered laser diode. The absence of a free space cavity makes the system stable over a base-plate temperature range of 30K. At the same time the use of a laser diode enables modulation of the pump wavelength by controlling the drive current. This is utilized to achieve a power modulation depth of >90% for the second harmonic light, with a rise time <40 µs.

The analytical comparison of pulses generated by locking three and five longitudinal modes in free-running class -B lasers

jafar jahanpanah and farzane sharafi

Doc ID: 273774 Received 15 Aug 2016; Accepted 17 Oct 2016; Posted 17 Oct 2016  View: PDF

Abstract: We here consider the coherent oscillation of five longitudinal modes which led to the coupling of modes in frequency domain and generation of short pulses in time domain. The aim is to audit the mechanism of mode locking in more detail by extending the analytical solution of Maxwell-Bloch equations of motion from three to five mode states. The characteristics of pulses including height, repetition, and duration have been calculated for a five-mode class B laser, and their changes are compared with respect to the three-mode state. The effects of other parameters such as the mean damping rate of cavity mirrors, the frequency detuning of cavity longitudinal modes, and the laser pumping rate have also been investigated. The central and adjacent modes supply the energy of pulses. The amplification gains of five oscillating modes together with their contribution amount in forming pulses are evaluated. It is finally demonstrated that the results satisfy the energy conservation law.

Scintillations of higher order laser beams in anisotropic atmospheric turbulence

Yahya Baykal, Xiaoling Ji, and Yujuan Luo

Doc ID: 274440 Received 24 Aug 2016; Accepted 17 Oct 2016; Posted 17 Oct 2016  View: PDF

Abstract: The scintillation index of higher order laser beams are examined when such beams propagate in anisotropic atmospheric turbulence.Anisotropy is introduced through non-Kolmogorov atmospheric turbulence. The scintillation index results are obtained by employing theRytov method solution, thus the results are valid for weak anisotropic atmospheric turbulence and for horizontal links. Variations in thescintillations are shown for various higher order laser modes against the changes in the optical source size, power law exponent ofanisotropic non-Kolmogorov spectrum, anisotropic factors and the link length. Our results can be used in the design of optical wirelesscommunication systems used between aeroplanes.


Loic Trompet, Arnaud Mahieux, Bojan Ristic, Severine Robert, Valérie Wilquet, Ian Thomas, Ann Vandaele, and Jean-Loup Bertaux

Doc ID: 275012 Received 02 Sep 2016; Accepted 17 Oct 2016; Posted 18 Oct 2016  View: PDF

Abstract: The SOIR instrument on board the ESA Venus Express spacecraft, an infrared spectrometer sensitive from 2.2 µm to 4.3 µm probed the atmosphere of Venus from June 2006 until December 2014. During this time it performed more than 750 solar occultations of the Venus mesosphere and lower thermosphere. A new procedure has been developed for the estimation of the transmittance in order to decrease the number of rejected spectra, to check that the treated spectra are well calibrated, and to improve the quality of the calibrated spectra by reducing the noise and accurately normalizing to the solar spectrum.


Youichi Bitou and Y Kondou

Doc ID: 275349 Received 07 Sep 2016; Accepted 15 Oct 2016; Posted 17 Oct 2016  View: PDF

Abstract: An angle-based deflectometric surface profiler has been improved for the measurement of transparent parallelplates. In the developed system, the unwanted beam reflected from the back surface of the transparent parallelplate is removed by ensuring that the beam is obliquely incident to the measurement surface; this is realized byusing a modified pentamirror unit comprising two mirrors installed at a predetermined angle to one another. Thesurface profile measurement of a transparent parallel plate with a repeatability of less than ±0.7 nm wassuccessfully achieved. A measurement accuracy of around 3 nm was reached by comparing the developed systemwith other scanning deflectometric profiler systems for the measurement of a silicon bar mirror with a length of300 mm.

Metal-enhanced fluorescence of single shell-isolated alloy metal nanoparticle

Chengyun Zhang, Qingyan Han, Caixia Li, Mingdi Zhang, Longxiang Yan, and Hairong Zheng

Doc ID: 275287 Received 06 Sep 2016; Accepted 14 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: Single silica-shell isolated Au-Ag alloy nanoparticle is employed for investigating metal enhanced fluorescence effect. Well dispersed alloy nanoparticles are prepared by facile chemical method, and the property of local surface plasmon resonance is controlled by adjusting the metal component of the alloy and shell thickness. The distance dependence of fluorescence enhancement for single Au-Ag alloy nanoparticle is studied systematically with different silica shell thickness ranging from 2 to 35 nm. The isolation shell not only adjusts the distance between metal surface and fluorophore emitters, but also improves the chemical stability of the metal particle.

A fractional Fourier transform-based description of the Talbot effect: application to analog signal processing

Hugues Guillet de Chatellus and Côme Schnebelin

Doc ID: 268506 Received 19 Jul 2016; Accepted 14 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: Talbot effect, or self-imaging, is a fascinating feature of Fresnel diffraction, where an input periodic wavefront is periodically recovered after specific propagation distances through the free space. Interestingly, the Fresnel propagator shows a great similarity to the fractional Fourier transform (FrFT). In this paper, we provide an interpretation of the Talbot effect in the frame of the FrFT and derive simple summation formulas between the FrFT of a function, and the function itself. In particular we show that both the FrFT and the Fourier transform (FT) of any input function can be generated by coherent addition of replicas of the function itself, multiplied by a quadratic phase term. Transposed into the temporal domain, these results may have important applications for real-time analog computation of the FrFT/FT of arbitrary signals.

Anisotropic power spectrum of refractive-index fluctuation in hypersonic turbulence

Jiangting Li, shaofei yang, Lixin Guo, and Cheng Mingjian

Doc ID: 269756 Received 06 Jul 2016; Accepted 14 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: Anisotropic power spectrum of the refractive-index fluctuation in hypersonic turbulence was obtained by processing the experimental image of hypersonic plasma sheath and transforming the generalized anisotropic von-Karman spectrum. The power spectrum suggested here can provide as good a fit to measured spectrum data for hypersonic turbulence as that recorded from the nano planar laser scattering image. Based on the newfound anisotropic hypersonic turbulence power spectrum, Rytov approximation were employed to establish the wave structure function and the spatial coherence radius model of electromagnetic beams propagation in hypersonic turbulence. The influence of hypersonic turbulence on electromagnetic beams increases with the increase of the variance of the refractive-index fluctuation, and the decrease of turbulence outer scale and anisotropy parameters. Enhancing the anisotropy characteristics of the hypersonic turbulence led to a significant improvement in the propagation performance of electromagnetic beams in hypersonic plasma sheath. The spatial coherence radius was much smaller than that in atmospheric turbulence. These results are fundamental to understanding electromagnetic wave propagation in hypersonic turbulence.

Minimum Bias Image Processing with a Distributed Aperture Millimeter Wave Imager

Joseph Mait, Charles Harrity, Richard Martin, Chris Schuetz, Shouyuan Shi, and Dennis Prather

Doc ID: 270731 Received 22 Jul 2016; Accepted 14 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: We present a model for noise generated in a two-channel millimeter-wave imaging system and use it to develop a phase switching scheme that generatesa minimum amount of noise in the difference image between the two channels. The method switches between 0 and π over half the apertures in a distributedaperture millimeter wave imager. Simulations and experiments validate that this approach improves performance over switching between 0 and a randomphase value. The improved performance is visually evident in imagesof an extended object.

ZnO/graphene/Ag composite as recyclable surface-enhanced Raman scattering substrates

Jie Zhang, xiaolei zhang, Yimin Ding, and Yong Zhu

Doc ID: 272975 Received 01 Aug 2016; Accepted 14 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: SERS- active substrates based on ZnO/Ag and ZnO/graphene/Ag were prepared via synthesis of ZnO nanorod arrays through the ZnO seed layers, followed by deposition of Ag nanoparticles (AgNPs) onto ZnO and ZnO/graphene surface using photocatalytic deposition. The hybrid structures were confirmed by scanning electron microscopy (SEM) and Raman spectroscopy. Rhodamine 6G (R6G) was used as the probe analyte. The experimental results indicated that the detection concentration level was 10^(-7) M with an enhancement factor of about 1.6×10^5. Additionally, the photocatalytic properties of ZnO/Ag and ZnO/graphene/Ag were exploited to recycle these substrates through UV-assisted cleaning.

Investigation on iterative multiuser detection physical layer network coding in two-way relay free-space optical links with turbulences and pointing errors

Zina Abu Almaalie, Fary Ghassemlooy, Manav R. Bhatnagar, Hoa Le Minh, Nauman Aslam, Shien-Kuei Liaw, and It Lee

Doc ID: 273079 Received 04 Aug 2016; Accepted 13 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: Physical layer network coding (PNC) improves the throughput in wireless networks by enabling two nodes to exchange information using a minimum number of time slots. The PNC technique is proposed for two-way relay channel free space optical (TWRC-FSO) communication with the aim of maximizing the utilization of network resources. The multi-pair TWRC-FSO is considered in this paper, where the single-antenna on each pair seek to communicate via a common receiver aperture at relay. Therefore, the chip-interleaving is adopted as a technique to separate the different transmitted signals at the relay node to perform PNC mapping. Accordingly, this scheme relies on the iterative multiuser (I-MUD) technique for detection of users at the receiver. The bit error rate (BER) performance of the proposed system is examined under the combined influences of atmospheric loss, turbulence-induced channel fading and the pointing errors (PEs). By adopting the joint PNC mapping with interleaving and coding technique, the BER results show that the proposed scheme can achieve a significant performance improvement against the degrading effects of turbulences and PEs. It is also demonstrated that a larger number of simultaneous users can be supported with this new scheme in establishing a communication link between multiple pairs of nodes in two time slots, thereby improving the channel capacity.

Effects of collection geometry variations on linear and circular polarization persistence in both isotropic-scattering and forward-scattering environments

J D Van Der Laan, Jeremy Wright, D Scrymgeour, Shanalyn Kemme, and Eustace Dereniak

Doc ID: 273256 Received 09 Aug 2016; Accepted 13 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: We present simulation and experimental results showing circular polarization is more tolerant of optical collection geometry (field of view and collection area) variations than linear polarization for forward-scattering environments. Circular polarization also persists superiorly in the forward-scattering environment compared to linear polarization by maintaining its degree of polarization better through increasing optical thicknesses. In contrast, both linear and circular polarizations are susceptible to collection geometry variations for isotropic-scattering (Rayleigh regime) environments, and linear polarization maintains a small advantage in polarization persistence. Simulations and measurements are presented for laboratory-based environments of polystyrene microspheres in water. Particle diameters were 0.0824 µm (for isotropic-scattering) and were 1.925 µm (for forward-scattering) with an illumination wavelength of 543.5 nm.

Airborne forward pointing UV Rayleigh lidar for remote clear air turbulence (CAT) detection: system design and performance

Patrick Vrancken, Martin Wirth, Gerhard Ehret, Hervé Barny, Philippe Rondeau, and Henk Veerman

Doc ID: 270899 Received 20 Jul 2016; Accepted 13 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: A high-performance airborne UV Rayleigh lidar system was developed within the European project DELICAT. With its forward-pointing architecture it aims at demonstrating a novel detection scheme for clear air turbulence (CAT) for an aeronautics safety application. Due to its occurrence in clear and clean air at high altitudes (aviation cruise flight level), this type of turbulence evades microwave radar techniques and in most cases coherent Doppler lidar techniques. The present lidar detection technique relies on air density fluctuations measurement and is thus independent of backscatter from hydrometeors and aerosol particles. The subtle air density fluctuations caused by the turbulent air flow demand exceptionally high stability of the setup and in particular of the detection system.This paper describes an airborne test system for the purpose of demonstrating this technology and turbulence detection method: a high-power UV Rayleigh lidar system is installed on a research aircraft in a forward-looking configuration for use in cruise flight altitudes. Flight test measurements demonstrate this unique lidar system being able to resolve air density fluctuations occurring in light-to-moderate CAT at 5 km or moderate CAT at 10 km distance. A scaling of the determined stability and noise characteristics shows that such performance is adequate for an application in commercial air transport.

Design of a Circular Polarization Imager for Contrast Enhancement in Rainy Conditions

Fei Liu, Xiaopeng Shao, Jie Xu, and Pingli Han

Doc ID: 272001 Received 20 Jul 2016; Accepted 13 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: We present the design of a circular polarization imager for imaging in rainy conditions, which is free from image calibration and correction before obtaining the orthogonal-state contrast image. The system employed a quarter wave plate in front of two Wollaston Prisms (WPs) to capture circularly polarized information and to acquire two orthogonally polarized images simultaneously on the Charge Coupled Device (CCD). Along with the WPs, a re-imaging part with multi-aperture structure composed of two separate specialized reimaging modules, were implemented to make sure the two orthogonally polarized intensity images are exactly indicating the same scene. Exploiting circularly polarized information provides advantages over linear polarization imaging system when considering the turbulence of media and illumination. Substantial data have demonstrated the effects of the novel designed polarization imaging system.

Managing focal fields of vector beams with multiple polarization singularities

Jianlin Zhao, Lei han, Sheng Liu, Peng Li, yi zhang, huachao cheng, and Xuetao Gan

Doc ID: 272011 Received 20 Jul 2016; Accepted 13 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: We explore the tight focusing behavior of vector beams with multiple polarization singularities, and analyze the influences of the number, position and topological charge of the singularities on the focal fields. It is found that the ellipticity of the local polarization states at the focal plane could be determined by the spatial distribution of the polarization singularities of the vector beam. When the spatial location and topological charge of singularities have even-fold rotation symmetry, the transverse fields at the focal plane are locally linearly polarized. Otherwise, the polarization state becomes a locally hybrid one. By appropriately arranging the distribution of the polarization singularities in the vector beam, the polarization distributions of the focal fields could be altered while the intensity maintains unchanged.

A Four-Core Optical Fiber as a Calorimetric Gauge

Naci Inci, Sema Güvenç, Belkıs Gökbulut, Gulsen Kosoglu, and Heba Yuksel

Doc ID: 272053 Received 20 Jul 2016; Accepted 13 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: A four-core optical fiber is demonstrated as a calorimetric gauge for investigation of one-dimensional heat transfer measurements. Transient heat pulses from a Nd:YAG laser of 600 ms duration with a repetition rate of the order of 10 s are delivered onto the cleaved distal end face of the four core fiber, aiming at one of the single cores only, which cause an optical path length difference between four guiding cores due to the temperature induced change in the index of refraction and physical length of the targeted fiber core in concern. This results in a shift in the fringe pattern, which is operated in the reflection scheme. A phase shift of 0.43±0.015 rad is measured with a CMOS camera for 40 mW pulses. The thermal heat diffusion length in the selected fiber core is determined to be 2.8 mm, which contains 10.9±0.38 kJ/m2s heat, causing a temperature rise of 1.43±0.05 K.

Improved LUT method of computer generated holograms

Ni Li, Hui Wei, and Guanghong Gong

Doc ID: 270183 Received 12 Jul 2016; Accepted 13 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: Heavy computation load and vast memory requirement are major bottlenecks of computer generated hologram (CGH) which is promising and challenging in 3D display. To solve these problems, an improved look-up table (LUT) method suitable for arbitrarily sampling object points is proposed and implemented on graphics processing unit (GPU) whose reconstructed object quality is consistent with that of the coherent ray trace (CRT) method. The concept of distance factor is defined and the distance factors are pre-computed off-line and stored in a look-up table. Results show that while retaining close reconstruction quality as the CRT method, the on-line computation time is dramatically reduced compared with the LUT method on GPU and the memory usage is lower than that of the N-LUT considerably. Optical experiments are carried out to validate the effectiveness of proposed method.

Efficient diode end-pumped acousto-optically Q-switched Nd:YAG/BaTeMo2O9 Raman laser

Fen Bai, qingpuq wang, Zhiyong Jiao, Xianfeng Xu, hui zhang, and xutangg tao

Doc ID: 270620 Received 18 Jul 2016; Accepted 13 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: BaTeMo2O9 (BTM) is employed to achieve efficient stimulated Raman scattering conversion in a diode end-pumped acousto-optically Q-switched Nd:YAG laser. With an incident diode power of 8.6 W, 732 mW of 1179 nm first-Stokes average output power was generated at a pulse repetition rate of 10 kHz, corresponding to a diode-to-Raman conversion efficiency of 8.5%.

Time resolved long-wave infrared laser-induced breakdown spectroscopy (LIBS) of inorganic energetic materials by a rapid LIBS mercury-cadmium-telluride (MCT) linear array detection system

Clayton Yang, Feng Jin, Sudhir Trivedi, Ei Brown, Uwe Hommerich, Jacob Khurgin, and Alan Samuels

Doc ID: 270715 Received 18 Jul 2016; Accepted 13 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: A MCT linear array detection system that is capable of rapidly capturing (~1–5 second) a broad spectrum of atomic and molecular LIBS emissions in the long-wave infrared region (LWIR, ~5.6 to 10 µm) was recently developed. Similar to the conventional Ultraviolet-Visible (UV-Vis) LIBS, a broad band emission spectrum of condensed phase samples covering 5.6 to 10 µm spectral region could be acquired from just a single laser-induced micro-plasma. Intense and distinct atomic and molecular LWIR emission signatures of various solid inorganic energetic materials were readily observed and identified. Time resolved emissions of inorganic energetic materials were studied to assess the lifetimes of LWIR atomic and molecular emissions. The LWIR atomic emissions decayed generally fast on the scale of tens of microseconds (µs) while the molecular signature emissions from target molecules excited by the laser-induced plasma appeared to be very long lived (~ millisecond). The time dependence of emission intensities and peak wavelengths of these signature emissions gave an insight into the origin and the environment of the emitting target species. Moreover, observed lifetimes of these LWIR emissions can be utilized for further optimization of the signal quality and detection limits of this technique.

Active thermal fine laser tuning in a broad spectral rangeand optical properties of cholesteric liquid crystal


Doc ID: 268652 Received 30 Jun 2016; Accepted 13 Oct 2016; Posted 13 Oct 2016  View: PDF

Abstract: In this study, we achieved active fine laser tuning in a broad spectral range with dye-doped cholesteric liquid crystal wedgetypecells through temperature control. Spatial pitch gradient of each position of the wedge cell at room temperature was almostmaintained after developing temperature gradient. To achieve the maximum tuning range, chiral dopant concentration,thickness, thickness gradient, and temperature gradient on the wedge cell should be matched properly. In order to understandthe laser tuning mechanism for temperature change, we studied the temperature dependence of optical properties of thephotonic band gap of cholesteric liquid crystals. In our cholesteric liquid crystal samples, when temperature was increased,photonic band gaps were shifted toward blue while the width of photonic band gap was decreased, regardless of whether thehelicity was left-handed or right-handed helicity. This is mainly due to the combination of decreased refractive indices, highermolecular anisotropy of chiral molecules, and increased chiral molecular solubility. We envisage that this kind of study willprove useful in the development of practical active tunable CLC laser devices.

A single-ended mid-infrared laser-absorption sensor for simultaneous in-situ measurements of H₂O, CO₂, CO, and temperature in combustion flows

Wen Yu Peng, Christopher Goldenstein, Mitchell Spearrin, Jay Jeffries, and Ronald Hanson

Doc ID: 270408 Received 27 Jul 2016; Accepted 13 Oct 2016; Posted 17 Oct 2016  View: PDF

Abstract: We present the development and demonstration of a four-color single-ended mid-infrared tunable laser-absorption sensor for simultaneous measurements of H₂O, CO₂, CO, and temperature in combustion flows. This sensor operates by transmitting laser light through a single optical port and measuring the backscattered radiation from a reflecting surface within the combustion device. Scanned-wavelength-modulation spectroscopy with second-harmonic detection and first-harmonic normalization (scanned-WMS-2f/1f) was used to compensate for the effects of non-absorption losses in the harsh environment. Two tunable diode lasers (TDLs) operating near 2551 and 2482 nm were utilized to measure H₂O concentration and temperature while an interband-cascade laser (ICL) near 4176 nm and a quantum-cascade laser (QCL) near 4865 nm were used for measuring CO₂ and CO, respectively. The lasers were modulated at either 90 kHz or 112 kHz and scanned across the peaks of their respective absorption features at 1 kHz, leading to a measurement rate of 2 kHz. A hybrid demultiplexing strategy involving both spectral filtering and frequency-domain demodulation was used to decouple the backscattered radiation into its constituent signals. Demonstration measurements were made in the exhaust of a laboratory-scale laminar methane-air flat flame burner at atmospheric pressure and equivalence ratios ranging from 0.7 to 1.2. A stainless steel reflective plate was placed 0.78 cm away from the sensor head within the combustion exhaust, leading to a total absorption path length of 1.56 cm. Detection limits of 1.4% H₂O, 0.6% CO₂, and 0.4% CO by mole were reported. To the authors' knowledge, this work represents the first demonstration of a mid-infrared laser-absorption sensor using a single-ended architecture in combustion flows.

Effective information processing method to produce computer-generated hologram based on spatial light modulator

Qiong-Hua Wang, su-juan liu, Di Wang, and song-jie li

Doc ID: 272370 Received 26 Jul 2016; Accepted 13 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: In this paper, we propose an effective information processing method to produce computer-generated hologram(CGH) based on the spatial light modulator (SLM). The method generates the CGH according to the property of thefield of view (FOV) and it has never been proposed before. The CGH is composed by the essential interferencepatterns (EIPs). Each EIP records the information of different object points. The resolution of the EIP is reduced. Inthe reconstructed process, the boundaries of the diffraction light of each EIP and FOV of the reconstructed imageare parallel with each other. Compared with the conventional method, the experiments demonstrate that theeffective reconstructed information in the FOV has no change, while the waste reconstructed information out of theFOV is decreased at any viewing distances. The CGH can reconstruct the image with high quality. Meanwhile, thecomputation burden of calculating the CGH is reduced in our method.

Piezo- and elasto-optic coefficients for calcium tungstate crystals

Oleksandr Sakharuk, Bohdan Mytsyk, Natalya Demyanyshyn, and Ivan Solskii

Doc ID: 272615 Received 27 Jul 2016; Accepted 13 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: General equation describing rotation of optical indicatrix of tetragonal crystals (4, 4, 4/m symmetry classes) around Х3 axis (optical axis) depending on direction of uniaxial pressure in the plane, perpendicular to crystal optical axis is written. Partial cases of general equation, when pressure is acting along Х1 (Х2) axis or along diagonal between Х1, Х2 axes are received. Values of piezo-optic coefficients (POCs) π61, π16 and π45 are determined by conoscopic method on the basis of appropriate equations. Other POCs πim are determined by interferometric method. All components of the matrix of elasto-optic coefficients are also determined as рin = πimCmn. These results are being compared to the ones received on the basis of wave-mechanical calculations. Objective рin values are necessary to build indicative surfaces of elasto-optic effect, to find maximums of these surfaces and appropriate maximum values of acousto-optic quality coefficients.

Nonlinear Polarization Spectroscopy of a Rydberg State for Laser Stabilization

David Meyer, Paul Kunz, and Neal Solmeyer

Doc ID: 272823 Received 01 Aug 2016; Accepted 13 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: We demonstrate modulation-free laser stabilization to an atomic Rydberg transition using nonlinear polarization spectroscopy. To stabilize a laser to the upper transition of a three-level ladder scheme, the techniques of standard polarization spectroscopy are adapted to use a narrow, nonlinear coherence feature. We obtain a sub-natural linewidth dispersive signal that is directly suitable for laser frequency stabilization. We examine the effect of laser polarization on the dispersive lineshape. This technique stabilizes the laser to an absolute frequency reference, can be used with numerous Rydberg levels, and eliminates laser modulation, which can enable high bandwidth feedback.

Miniaturized LED primary optics design used for short distance color mixing

Tsung-Xian Lee, Meng-Che Tsai, Shuo-Chieh Chang, and Kuei-Chun Liu

Doc ID: 273849 Received 17 Aug 2016; Accepted 13 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: Color-tunable LED light fixtures generally change colors by controlling LEDs of multiple colors. This type of light source requires additional secondary optics and light-mixing distances to deliver color-mixing functions and perform high color uniformity. However, the increases in color-mixing areas may limit the difficulty and the extreme application of the tiny lighting fixtures. Therefore, in this study, we introduce a LED primary optics design method that retains standard LED package size while featuring a color-mixing chamber. This method combines a freeform lens with a zigzag structure by using double total internal reflection to disperse light uniformly. In contrast to a typical hemispherical lens, our design effectively lowers the weighted average color difference from 0.03 to 0.0035, and maintains optical efficiency of at least 90% at distances of up to 20mm without using any optical diffuser.

Analysis of surface deformation in thin film coatings by carrier frequency interferometry

Elzbieta Jankowska, Sławomir Drobczyński, and Carmen Menoni

Doc ID: 274505 Received 25 Aug 2016; Accepted 13 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: We demonstrate a method based on carrier frequency interferometry (CFI) that measures surface deformation with high accuracy. The method is applied to assess deformation of thin film dielectrics deposited on thick substrates. CFI measured the wavefront radius of curvature R with an accuracy of 0.2% for R smaller than 500 m and 2% for R between 500 and 2000 m (flat reference substrate). We show the method has a significantly larger dynamic range and sensitivity than Twyman-Green, and comparable sensitivity to white light interferometry.

Investigation of SiO2-Al2O3-nanolaminates for protection of silver reflectors

Stefan Schwinde, Mark Schuermann, Norbert Kaiser, and Andreas Tünnermann

Doc ID: 274888 Received 30 Aug 2016; Accepted 13 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: H2S and particles from the atmosphere can damage silver reflectors. These defects lead to scattering and a reduction of reflectivity. With regard to these risks, the suitability of sputtered SiO2, Al2O3 and SiO2-Al2O3-nanolaminates for the protection of Ag was analyzed. The optical properties, protection properties against H2S, solubility, film stress, and the protection properties against particle-induced defect formation have been investigated. Especially in the case of particle-induced defects on protected Ag, differences between the protective coatings are considerable and the nanolaminate layers have advantageous properties.

3D- shape recognition and size measurement ofirregular rough particles using multi-viewsinterferometric out-of-focus imaging

Lila Ouldarbi, Mohamed Talbi, Sebastien Coetmellec, Denis Lebrun, Gerard Grehan, Gaele Perret, and Marc Brunel

Doc ID: 272030 Received 20 Jul 2016; Accepted 12 Oct 2016; Posted 13 Oct 2016  View: PDF

Abstract: We realize simplified-tomography experiments on irregular rough particles using interferometric out-of-focusimaging. Using two angles of view, we determine the global 3D-shape, the dimensions, and the 3D-orientation ofirregular rough particles whose morphologies belong to some families as sticks, plates, cross.

Phase-change photonic-crystal switch divider based on Ge2Sb2Te5 thin films

Beijiao Ma, Peiqing Zhang, Hui Wang, Tengyu Zhang, Jianghui Zeng, qian zhang, Guoxiang Wang, XU PEIPENG, Wei Zhang, and Shixun Dai

Doc ID: 272742 Received 29 Jul 2016; Accepted 12 Oct 2016; Posted 13 Oct 2016  View: PDF

Abstract: A three-port phase-change photonic-crystal switch divider based on Ge2Sb2Te5 chalcogenide thin film was proposed. The chalcogenide material used was determined to have a high refractive index and fast phase-change speed by using laser radiation. The structure with a T-junction cavity was used to achieve three switch functions: switching “ON” in only one output port, switching “OFF” in both output ports, and dividing signals into two output ports. The transmission properties of the designed device at 2.0 µm were studied by the finite difference time domain method, which showed that the switch divider can achieve very high switching efficiency by optimizing T-junction cavity parameters. The scaling laws of photonic crystals revealed that the operating wavelength of the designed structure can be easily extended to another wavelength in the mid-infrared region.

Centroid stabilization for laser alignment to corner cubes: designing a matched filter

Abdul Awwal, Erlan Bliss, Gordon Brunton, Victoria Miller Kamm, Richard Leach, Roger Lowe-Webb, Randy Roberts, and k wilhelmsen

Doc ID: 273018 Received 04 Aug 2016; Accepted 12 Oct 2016; Posted 13 Oct 2016  View: PDF

Abstract: Automation of image-based alignment of NIF high energy laser beams is providing the capability of executing multiple target shots per day. One important alignment is beam centration through the second and third harmonic generating crystals in the final optics assembly (FOA), which employs two retro-reflecting corner cubes as centering references for each beam. Beam-to-beam variations and systematic beam changes over time in the FOA corner-cube images can lead to a reduction in accuracy as well as increased convergence durations for the template-based position detector. A systematic approach is described that maintains FOA corner cube templates and guarantees stable position estimation.

Influence of Thermal Deformation of Multilayer Dielectric Grating on Spectrally Combined Beam

Bin Zhang, Lei Yang, and Zhen Wu

Doc ID: 274040 Received 17 Aug 2016; Accepted 12 Oct 2016; Posted 13 Oct 2016  View: PDF

Abstract: In spectral beam combining (SBC) systems, temperature rise inevitably happens to the multilayer dielectric grating (MDG) due to irradiation of high power continue-wave(CW) laser, resulting in the thermal deformation of the MDG, and further the degradation of the characteristics of the combined beam due to the thermal deformation of the grating. The calculation model of thermal deformation of the MDG has been proposed and the distributions of temperature field and thermal deformation of the grating have been analyzed. On this basis, a propagation model of SBC system has further been built up. By utilizing the diffraction integral method and the principle of incoherent superposition, the intensity distribution and the beam quality of the combined beam with different power density based on the MDG have been numerically calculated and analyzed in detail. The results show that both the maximum temperature rise and the thermal deformation of the MDG increase dramatically with the increasing power density of the incident laser beam. Side lobes presents in the intensity distribution of the combined beam due to the thermal deformation of the MDG. Furthermore, the side lobes of the combined beam become increasingly obvious with the increasing power density. Additionally, the beam quality of the combined beam degrades significantly with the increasing power density of the incident laser beam.

Ytterbium-doped Q-switched fiber laser based upon manganese dioxide (MnO2) saturable absorber

Haroldo Hattori, Abdul Khaleque, Liming Liu, and Michael Greck

Doc ID: 274324 Received 23 Aug 2016; Accepted 12 Oct 2016; Posted 13 Oct 2016  View: PDF

Abstract: Manganese dioxide (MnO2) is an abundant material that is widely used in many devices such as alkaline batteries.At infrared frequencies, manganese dioxide is lossy and strongly absorbs light. These characteristics make MnO2 apotential candidate for low cost saturable absorber in Q-switched lasers. In this article, we examine theperformance of MnO2 as saturable absorber in an ytterbium-doped Q-switched fiber laser: we show that it canproduce pulses with durations ranging from 300 ns to 1800 ns.

Reconstruction of the Optical System of Personalized Eye Models by using Magnetic Resonance Imaging

Chi-hung Lee, Han-Ying Sun, and Chun-Chao Chuang

Doc ID: 270133 Received 25 Jul 2016; Accepted 12 Oct 2016; Posted 12 Oct 2016  View: PDF

Abstract: This study presents a practical method for reconstructing the optical system of personalized eye models by using magnetic resonance imaging (MRI). Monocular images were obtained from a young (20-year-old) healthy subject viewing at a near point (10 cm). Each MR image was first analyzed using several commercial softwares to capture the profile of each optical element of the human eye except for the anterior lens surface, which could not be determined because it overlapped the ciliary muscle. The missing profile was substituted with a modified profile from a generic eye model. After the data—including the refractive indices from a generic model—were input in ZEMAX, we obtained a reasonable initial layout. By further considering the resolution of MRI, the model was optimized to match the optical performance of a healthy eye. The main benefit of having a personalized eye model is the ability to quantitatively identify wide-angle ocular aberrations, which were corrected by the designed free-form spectacle lens.

High-speed time-resolved laser scanning microscopy using line-to-pixel referencing method

Jiheun Ryu, Jayul Kim, Hyunjun Kim, Jae-heon Jeong, Hak-jun Lee, Hongki Yoo, and Dae-Gab Gweon

Doc ID: 273432 Received 08 Aug 2016; Accepted 12 Oct 2016; Posted 12 Oct 2016  View: PDF

Abstract: Time-resolved laser scanning microscopy can visualize photo-physical characteristics of a biological specimen. Conventional techniques, which can be represented by time-correlated single-photon counting (TCSPC), acquire an image through long-time accumulation of single-photons. Therefore, many high-speed techniques have been reported to monitor and analyze a real-time variation of such characteristics in vivo. Among them, the analog mean-delay (AMD) method is a cost-effective way to enhance photon-accumulation speed by direct calculation of average arrival time of the photon flux rather than stochastic accumulation of each single photon. However, the image acquisition speed, in terms of pixel rate, of the AMD method is still limited by the pulse repetition rate. In this paper, we propose a high-speed time-resolved laser scanning microscopy, which adopts a novel method for real-time temporal referencing. Using a pulsed laser with 40-MHz repetition rate as light source, a frame rate of 3.73 fps with a pixel rate of 3.91 MHz was accomplished while maintaining the measurement precision under 20 ps.

Reflectivity Mapping of Large-aperture Mirrors with Cavity Ring-down Technique

Bincheng Li, Yanling Han, Lifeng Gao, and Sheng-Ming Xiong

Doc ID: 274170 Received 22 Aug 2016; Accepted 12 Oct 2016; Posted 12 Oct 2016  View: PDF

Abstract: A high-precision reflectivity measurement device based on an optical-feedback cavity ring-down technique is developed for mapping reflectivity distributions of large-aperture highly- reflective (HR) mirrors with diameter up to 300 mm. Reflectivity maps are obtained by two-dimensionally raster-scanning the large-aperture mirrors and measuring the reflectivity as a function of position. By employing a laser source with beam diameter approximately 0.4mm, reflectivity maps with sub-millimeter spatial resolution is achieved. The reflectivity non-uniformity of HR mirrors is investigated by statistically analyzing the experimental reflectivity distributions. The measurement repeatability of the device is also experimentally investigated, with standard deviation of approximately 0.0001% for reflectivity higher than 99.99%.

Mechanical Properties of PEALD Metallic Oxides for Optical Applications

Adriana Szeghalmi, Svetlana Shestaeva, Peter Munzert, Astrid Bingel, Lilit Ghazaryan, Andreas Tünnermann, and Christian Patzig

Doc ID: 274357 Received 23 Aug 2016; Accepted 12 Oct 2016; Posted 12 Oct 2016  View: PDF

Abstract: Structural, optical, and mechanical properties of Al2O3, SiO2, and HfO2 materials prepared by plasma enhanced atomic layer deposition (PEALD) were investigated. Residual stress poses significant challenges for optical coatings since it may lead to mechanical failure, but in-depth understanding of these properties is still missing for PEALD coatings. The tensile stress of PEALD alumina films decreases with increasing deposition temperature and is approximately 100 MPa lower than the stress in thermally grown films. It was associated with incorporation of -OH groups in the film as measured by infrared spectroscopy. The tensile stress of hafnia PEALD layers increases with deposition temperature and was related to crystallization of the film. HfO2 nanocrystallites were observed even at 100°C deposition temperature with transmission electron microscopy (TEM). Stress in hafnia films can be reduced from approx. 650 MPA to approx. 450 MPa by incorporating ultrathin Al2O3 layers. PEALD silica layers have shown moderate stress values and stress relaxation with the storage time, which was correlated to water adsorption. A complex interference coating system for a dichroic mirror (DCM) at 355 nm wavelength was realized with a total coating thickness of ca. 2 m. Severe cracking of the DCM coating was observed, and it propagates even into the substrate material, showing a good adhesion of the ALD films. The reflectance peak is above 99.6% despite the mechanical failure, and further optimization on the material properties should be carried out for demanding optical applications.

Reactive Dynamics Analysis of Critical Nb2O5 Sputtering Rate for Drum Based Metal-like Deposition

Shigeng Song, CHENG LI, Hin On Chu, and Des Gibson

Doc ID: 274926 Received 30 Aug 2016; Accepted 11 Oct 2016; Posted 11 Oct 2016  View: PDF

Abstract: Drum based metal-like film deposition for oxide was investigated using single wavelength in-situ monitoring. The data was used to investigate oxidation mechanism using combined second order kinetic and parabolic models. A critical Nb2O5 deposition rate of 0.507nm/s was found at drum rotation 1rev/s. However, N2O5 samples prepared at varying deposition rates showed deposition rate must be much lower than critical deposition rate to achieve reasonable absorption. Thus simulation for volume-fraction of metal in oxide layer was done using EMA and distribution function. Simulation gave high agreement with experimental results, and allows prediction of extinction coefficients at various deposition rates.

3D-imaging: A scanning light pattern projector

Michael Jakobsen, Mathias Stokholm, Steen Hanson, Rasmus Kjær, and Thomas Allin

Doc ID: 269499 Received 30 Jun 2016; Accepted 11 Oct 2016; Posted 12 Oct 2016  View: PDF

Abstract: The technology of electro wetting dielectric surfaces can be used to electrically alter the optical parameters of liquid lenses. With several adequately arranged electrodes, both the curvature and the 2D tilt of a membrane between two liquids can be controlled. Thus, both the focal length and the tilt of this lens can be adjusted electrically. A tilt of the curved surface can be considered as a transverse shift of the lens, and therefore incident light will be deflected accordingly. Specifically, the tilting ability of the liquid lens will be tested by combining the liquid lens with a projector in order to scan lines across an object. Finally, the liquid lens and the projector in combination with four stereo cameras will be demonstrated as a 3D imaging setup.

Characteristics and Crosstalk of Optical Waveguides Fabricated in PMMA Circuit Board

Hanan Hamid, Christian Haunhorst, David Thiel, and Thomas Fickenscher

Doc ID: 266924 Received 25 May 2016; Accepted 11 Oct 2016; Posted 11 Oct 2016  View: PDF

Abstract: Electro-optical circuit boards should provide simple and cost effective coupling techniques and crosstalk levels less than -30 dB. A dicing saw was used to create waveguide grooves with a surface roughness of less than 183 nm in a 1.6 mm thick polymethyl methacrylate polymer (PMMA) substrate. The buried optical waveguides were made from SU-8 in a PMMA substrate covered with a 1 mm PMMA sheet. The propagation loss for a 500 μm × 570 μm straight waveguide was 0.9 dB/cm at 1310 nm. The coupling between parallel waveguides was measured at separation distances from 45 to 595 µm. The crosstalk was less than -40 dB for 65 mm long waveguides. This fabrication method shows potential for dense optical interconnects with very low crosstalk.

Liquid index matching for 2D and 3D terahertz imaging

Patrick Mounaix, Jean-Baptiste Perraud, Joyce Sleiman, Benoit RECUR, Hugo Balacey, François Simoens, and Jean-Paul Guillet

Doc ID: 268695 Received 21 Jun 2016; Accepted 11 Oct 2016; Posted 11 Oct 2016  View: PDF

Abstract: 2D terahertz imaging and 3D visualization suffer from severe artifacts since an importantpart of the terahertz beam is reflected, diffracted and refracted at each interface. These phenomena aredue to refractive index mismatch and reflection in the case of non-orthogonal incidence. This paperproposes experimental procedure that reduces these deleterious optical refraction effects for acylinder and a prism made with polyethylene material. We insert these samples in a low absorptionliquid medium to match the sample index. Then the surrounding air is replaced by a liquid with anoptimized refractive index with respect to the samples under studied. This approach allows us torecover more accurately the original sample shape by time of flight tomography.

Efficient self-stimulated Raman scattering with simultaneously self-mode-locking in a diode-pumped Nd:GdVO4 laser

Jiying Peng, Zuohan li, Jian-Quan Yao, Ming Han, and linghong jiang

Doc ID: 270051 Received 20 Jul 2016; Accepted 11 Oct 2016; Posted 11 Oct 2016  View: PDF

Abstract: We demonstrated an efficient diode-pumped picosecond self-Raman Nd:GdVO4 laser with the simultaneousprocesses of stimulated Raman scattering and self-mode locking in a same crystal. The design of self-mode lockedwas theoretically analyzed, and a compact and feasible dual-concave cavity was adopted. The maximum outputpower of first-Stokes Raman laser was 736 mW with the repetition rate of 1.51 GHz. Besides, the second harmonicgeneration of yellow laser at 586.5 nm is accomplished with an external LiB3O5 crystal.

Multi-subzone algorithm for absolute phase retrieval in digital fringe projection profilometry

Chenggen Quan, Yidan Xing, and C Tay

Doc ID: 272392 Received 26 Jul 2016; Accepted 11 Oct 2016; Posted 11 Oct 2016  View: PDF

Abstract: Codewords are important in encoded absolute phase retrieval techniques such as two-frequency, gray-code, and phase-coding techniques. Each sinusoidal fringe is marked by a unique codeword so that an absolute fringe order can be determined by decoding the codeword. However, due to limited number of unique codewords, sinusoidal fringe patterns do not contain high-frequency fringes without the use of additional patterns. A multi-subzone coding and decoding algorithm is thus proposed to overcome the limitation. Three multi-subzone coding methods based on two-frequency, gray-code, and phase-coding techniques are presented. The coding creates multiple subzones of unique codewords and the decoding enables it to use non-unique codewords to identify absolute fringe order. Specifically, the range of fringe order is estimated by the use of a wrapped phase map and the absolute fringe order is identified by a codeword. Experimental studies demonstrate the advantages of the proposed algorithm over existing coding methods. The proposed algorithm is suitable for measuring objects with large step-height surface discontinuities.

High efficiency, 154 W CW, diode-pumped Raman fiber laser with brightness enhancement

Yaakov Glick, Viktor Fromzel, Jun Zhang, Nikolay Ter-Gabrielyan, and Mark Dubinskii

Doc ID: 272651 Received 04 Aug 2016; Accepted 11 Oct 2016; Posted 11 Oct 2016  View: PDF

Abstract: We demonstrate a high power high efficiency Raman fiber laser pumped directly by laser diode modules at 978 nm. 154 Watts of CW power were obtained at a wavelength of 10 nm with an optical to optical efficiency of 65%. A commercial graded-index (GRIN) core fiber acts as the Raman fiber in a power oscillator configuration which includes spectral selection to prevent generation of the 2nd Stokes. In addition, brightness enhancement of the pump beam by a factor of 8.4 is attained due to the Raman gain distribution profile in the GRIN fiber. To the best of our knowledge this is the highest power and highest efficiency Raman fiber laser demonstrated in any configuration allowing brightness enhancement (i.e in either cladding pumped configuration or with GRIN fibers, excluding step index core pumped), regardless of pumping scheme (i.e. either diode pumped or fiber laser pumped).

Envelope-Based Technique for Liquid Level Sensors using In-Line Fiber Mach-Zehnder Interferometer

Camilo Rodriguez, Moises Ribeiro, Anselmo Frizera-Neto, Carlos Schmidt Castellani, and Maria Pontes

Doc ID: 274659 Received 26 Aug 2016; Accepted 10 Oct 2016; Posted 11 Oct 2016  View: PDF

Abstract: This paper proposes a novel sensor interrogation technique based on the analysis of the overall spectrum envelope of an in-line Mach-Zehnder interferometer structure with three different fibers. The interference pattern created by a level sensor of 120 mm was evaluated with both the traditional and the proposed interrogation techniques. The result shows that the technique here proposed improves the sensitivity of the sensor by more then an order of magnitude. Moreover, our new interrogation technique allows the length of an in-line Mach-Zehnder interferometer to be extended up to 470 mm maintaining high linearity and sensitivity.

Numerical investigation on flat-topped vortex hollow beams and Bessel beams propagating in turbulent atmosphere

XiuHua Yuan, Yalin Zhang, Donglin Ma, and Zeyu Zhou

Doc ID: 273573 Received 15 Aug 2016; Accepted 10 Oct 2016; Posted 10 Oct 2016  View: PDF

Abstract: In this paper, the aperture averaged scintillation, mean signal-to-noise ratio (SNR) and average bit error rate (BER) for both the flat-topped vortex hollow beams and Bessel beams propagating in turbulent atmosphere are evaluated. Investigations are also made illustrating the variation of aperture averaged scintillation, mean SNR and average BER against the beam type, propagation distance and size of the receiver aperture. Compared with the flat-topped vortex hollow beams, the Bessel beams have smaller aperture averaged scintillation, higher mean SNR and the lower average BER under the same conditions.

Fabrication-Friendly Subwavelength-Structure-Assisted Waveguide for Dispersion Engineering

Abbas Zarifkar and Zeinab Jafari

Doc ID: 275936 Received 15 Sep 2016; Accepted 10 Oct 2016; Posted 11 Oct 2016  View: PDF

Abstract: A subwavelength structure deposited on top of a silicon strip is utilized as a novel tool for dispersion engineering. The equivalent refractive index of the subwavelength structure can be tailored through adjusting its period and duty cycle. As finding suitable materials with both appropriate refractive index and fabrication compatibility is one of the main difficulties in dispersion engineering, the possibility of the refractive index engineering is the most significant advantage of the proposed waveguide. It can be beneficial for controlling the properties of the fundamental quasi-TM mode and consequently its dispersion characteristics without any concern about material compatibility. Utilizing this waveguide geometry, a wide and flattened low dispersion bandwidth can be achieved. Moreover, high anomalous and normal dispersion is realizable without any degradation in dispersion flatness over bandwidth. Therefore, the proposed waveguide structure is promising for dispersion tailoring in both linear and nonlinear applications.

Thin-wall tubes for coupling THz waves to metal wires

Huawei Liang, Yingxue Huang, Min Zhang, Hong Su, Ling Li, and Shuangchen Ruan

Doc ID: 274055 Received 17 Aug 2016; Accepted 10 Oct 2016; Posted 12 Oct 2016  View: PDF

Abstract: Bare metal wires are among the most promising waveguides for guiding THz surface plasmon polaritons. In this study, a thin-wall tube is proposed for coupling THz waves to a metal wire with ultra-high efficiency, which results from three high mode matching for the two waveguides: field distributions, polarization directions and wave vectors. According to the mode-overlap calculation, the coupling efficiency can be always between 84% and 94% when the frequency of THz waves is in the range of 0.2 ~ 3 THz and the metal wire radius is 0.5 mm. The maximum efficiency is as high as 94% at 0.5 THz, which is much higher than that obtained by the previous methods. We further conclude that the optimal coupling efficiency can be obtained when the outer tube radius is equal to the wire radius and simultaneously the real propagation constants of modes in the two waveguides are the same.

A Novel MOEMS Accelerometer Based on Intensity Modulation by Using a One-Dimensional Photonic Crystal

Kambiz Abedi, Arash Sheikhaleh, kian Jafari, and Reza Gholamzadeh

Doc ID: 268818 Received 06 Jul 2016; Accepted 10 Oct 2016; Posted 10 Oct 2016  View: PDF

Abstract: In this paper, a novel sensitive MOEMS accelerometer based on intensity modulation is proposed by using a one-dimensional photonic crystal. Optical sensing system of the proposed structure includes an air-dielectric multilayer Photonic Band Gap (PBG) material, a LD light source, a typical photodiode (1550 nm) and a set of integrated optical waveguides. The proposed sensor provides several advantages such as relatively wide measurement range, good linearity in the whole measurement range, integration capability, negligible cross-axis sensitivity, high reliability and low air-damping coefficient which results in a wider frequency bandwidth for a fixed resonance frequency. Simulation results show that the functional characteristics of the sensor are as follows: a mechanical sensitivity of 119.21 nm/g, a linear measurement range of ±38 g and a resonance frequency of 1444 Hz. Thanks to the above characteristics, the proposed MOEMS accelerometer is suitable for a wide spectrum of applications ranging from consumer electronics to aerospace and inertial navigation.

Production of Brewster-angle thin film polarizers using ZrO2/SiO2 pair of materials

Alexander Tikhonravov, Valery Zhupanov, Ivan Kozlov, V. Fedoseev, Pavel Konotopov, and Michael Trubetskov

Doc ID: 272701 Received 29 Jul 2016; Accepted 10 Oct 2016; Posted 10 Oct 2016  View: PDF

Abstract: Production of polarizers for high-intensity applications based on ZrO2/SiO2 pair of thin film materials is discussed. A special approach to the accurate determination of ZrO2 refractive index and application of direct broad band optical monitoring enable obtaining good manufacturing results.

A metric for evaluation of filters efficiency in spectral cameras

Mohammad Amani Tehran and Alireza Mahmoudi Nahavandi

Doc ID: 269083 Received 24 Jun 2016; Accepted 09 Oct 2016; Posted 10 Oct 2016  View: PDF

Abstract: Although, metric functions which show the performance of a colorimetric imaging device have been investigated,metric for the analysis performance of a set of filters in wideband filter based spectral cameras has rarely beenstudied.Based on generalization of Vora’s “Measure of Goodness” (MOG) and Spanning Theorem, a single function metricwhich estimates the effectiveness of a filter set is introduced. The improved metric, named MMOG, varies betweenone, for a perfect and zero, for the worst possible set of filters. Results showed that MMOG exhibits more similartrend with mean square of spectral reflectance reconstruction errors than the Vora’s MOG index and it is robust tonoise in the imaging system. MMOG as a single metric could be exploited for the further analysis of manufacturingerrors.

The use of photoacoustic excitation and laser vibrometry to remotely detect trace explosives

Charles Wynn, Robert Haupt, John Doherty, Roderick Kunz, Wenyu Bai, and Gerald Diebold

Doc ID: 272085 Received 22 Jul 2016; Accepted 09 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: In this paper we examine a new laser-based approach to remotely initiate, measure, and differentiate acoustic and vibrational emissions from trace quantities of explosives materials against their environment. Using a pulsed ultraviolet laser (266 nm), we induce a significant (> 100 Pa) photoacoustic response from small quantities of military-grade explosives. The photoacoustic signal, with frequencies predominantly between 100-500 kHz, is detected remotely via a wideband laser Doppler vibrometer. This 2-laser system can be used to rapidly detect and discriminate explosives from ordinary background materials, which have significantly weaker photoacoustic response. A 100 ng/cm2 limit of detection is estimated. Photoablation is proposed as the dominant mechanism for the large photoacoustic signals generated by explosives.

Performance of multi-hop parallel free-space optical communication over gamma-gamma fading channel with pointing errors

Zhengguang Gao, Hongzhan Liu, Xiaoping Ma, and Wei Lu

Doc ID: 273580 Received 12 Aug 2016; Accepted 08 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: The multi-hop parallel relaying is considered in free-space optical (FSO) communication system deploying binary phase-shift keying (BPSK) modulation under the combined effects of gamma–gamma (GG) distribution and misalignment fading. Based on the best path selection criterion, the cumulative distribution function (CDF) of this cooperative random variable is derived. Then the performance of this optical mesh network is analyzed in detail. Monte Carlo simulation is also conducted to demonstrate the effectiveness of the results for the average bit error rate (ABER) and outage probability. The numerical result proves that it needs a smaller average transmitted optical power to achieve the same ABER and outage probability when using multi-hop parallel network in FSO links. Furthermore, the system using more number of hops and cooperative paths can improve the communication’s quality.

The hyperspectral characteristics analysis for leaf nitrogen content in different growth stages of winter wheat

hongchun zhu and Haiying LIU

Doc ID: 270117 Received 11 Jul 2016; Accepted 08 Oct 2016; Posted 10 Oct 2016  View: PDF

Abstract: The spectral characteristics in the range of visible light and near infrared shortwave (400-1000nm) are analyzed using the ground measured hyperspectral data and leaf nitrogen content(LNC) data of different growth stages of winter wheat, which were acquired in 2013 and 2015. Firstly, the quantitative models for monitoring the LNC at different growth stages of winter wheat were established using the main vegetation nitrogen spectral indices. Through analyzing the models’ simulation coefficient, it is proved that the quantitative correlation between LNC and spectral indices is incredible. So, vegetation nitrogen spectral indices should not be an effective quantitative estimating for winter wheat LNC. Secondly, a method for selecting representation wavebands of hyperspectral data sensitive to the LNC of winter wheat is proposed using spectral correlation as basis. The representation wavebands of hyperspectral data which were acquired in 2015 and sensitive to the LNC of winter wheat are determined using this method. Based on the acquired representation wavebands corresponding different growth stages of winter wheat, the quantitative models for monitoring the LNC at different growth stages of winter wheat were established using the data which acquired in 2015 and 2013. The results show that: the acquired representation wavebands combination corresponding different growth stages of winter wheat are different, and their red edge effect are obvious. The quantitative models for monitoring the LNC based on the representation wavebands are effective and credible. This research results laid the foundation of accurately quantitative monitoring for winter wheat LNC.

Measurement of the refractive index of electrically poled soda-lime glass layers using leaky modes

Robert Oven

Doc ID: 270345 Received 11 Jul 2016; Accepted 07 Oct 2016; Posted 10 Oct 2016  View: PDF

Abstract: Electrically poled layers have been formed in soda-lime glass using graphite electrodes in air. The refractive index and thickness of the poled glass layers have been measured by the analysis of leaky optical modes. These modes are supported by the poled layer and can be determined by analysis of the optical reflectivity measured with a prism coupler arrangement. A relatively constant refractive index ~ 1.486 in the poled glass region is measured, which is ~0.03 below the substrate index. The reflectivity data shows that the transition between poled and un-poled glass is very sharp and is consistent with ion transport models. The thickness of the poled glass region is consistent with the removal of Na+ and K+ ions from the poled region. The index and depth data is confirmed by interferometric measurements. The tensile stress in the poled glass layer is also estimated from optical birefringence measurements and is estimated to be ~0.3 GN/m2.

Thin-disk laser scaling limit due to thermal-lens induced misalignment instability

Karsten Schuhmann, Klaus Kirch, Francois Nez, Randolf Pohl, and aldo antognini

Doc ID: 272817 Received 01 Aug 2016; Accepted 07 Oct 2016; Posted 10 Oct 2016  View: PDF

Abstract: We present an obstacle in power scaling of thin-disk lasers related with self-driven growth of misalignment due to thermal lens effects. This self-driven growth arises from the changes of the optical phase difference at the disk caused by the excursion of the laser eigen-mode from the optical axis. We found a criterion based on a simplified model of this phenomenon which can be applied to design laser resonators insensitive to this effect.

Matching long period grating modes and localized plasmon resonances: effect on the sensitivity of the grating to the surrounding refractive index

José Fabris, Bárbara Heidemann, Júlia Pereira, Ismael Chiamenti, Marcela Oliveira, and Marcia Muller

Doc ID: 272086 Received 22 Jul 2016; Accepted 07 Oct 2016; Posted 10 Oct 2016  View: PDF

Abstract: The sensitivity and dynamical range of an optical fiber transducer consisting of a long period grating coated with gold nanoparticles is investigated. For a grating with an 80 µm spatial periodicity, the resonances close to the turning point lie within the 450–900 nm spectral range. Employing a bottom-up production route, the localized surface plasmon resonance of gold nanoparticles is matched to the grating resonances; it is shown that this results in an increase in the refractive index sensitivity of the device. The device also shows increased dynamic range and enhanced refractive index sensitivity in water.

Detectorless measurements of the operational linewidth of NIR VCSELs by Self-Mixing Interferometry

maria carmela cardilli and Maurizio Dabbicco

Doc ID: 273566 Received 10 Aug 2016; Accepted 07 Oct 2016; Posted 10 Oct 2016  View: PDF

Abstract: Self-mixing based on Vertical Cavity Surface Emitting Lasers (VCSEL), offers a compact and low-cost coherentdetection scheme for interferometric accessible measurements. The direct detection of the change in the junctionvoltage, in contrast to the traditional optical detection method by means of external photodiode, simplifies furtherthe setup by adding detector-less capability. The linewidth of a NIR VCSEL was estimated by using the methodbased on the statistical analysis of the Laser Self-Mixing fringe period in the moderate feedback regime. Weinvestigate the junction voltage noise and optical power noise, simultaneously acquired, in order to establish thebest operational condition for both detection schemes. When comparing the laser linewidth measured by thetraditional optical power modulation with that of the detector-less voltage self-mixing signal, the agreement iswithin the experimental errors.

Measurement of microfibril angles in bamboo usingMueller matrix imaging

Sumit Basu, Sayyad Mannan, Mohammad Zaffar, and Asima Pradhan

Doc ID: 273238 Received 09 Aug 2016; Accepted 06 Oct 2016; Posted 10 Oct 2016  View: PDF

Abstract: The microfibril angle (MFA) giving orientation of cellulose chains in hard sclerenchymatous bamboo fibresis one of the most important parameters determining overall strength of the bamboo culm. In thiswork, Mueller matrix imaging polarimetry is implemented for determining MFA measured over transversesection of group of fibres and parenchyma cells in bamboo of Dendrocalamus Strictus species. Themethod, based on Stokes-Mueller formalism, decouples the birefringence exhibited by crystalline cellulosefrom the clumped polarization parameters using sixteen images taken with different polarizationstates at sub-cellular resolution. Retardance values, obtained from polar decomposition of Mueller matrix,are extracted from different locations in the specimen and distribution of MFA over entire section ispresented. The method permits simultaneous measurement of MFA in transverse section of several fibresand parenchyma cells. The range of MFA obtained for bamboo fibres from Mueller matrix imaging isverified with the results obtained through X-ray diffraction using pole figure method.

Off-axis three-mirror freeform telescope with largelinear field of view based on integration mirror

Qingyu Meng, Hongyuan Wang, Kenjun Wang, Yan Wang, Zhenhua Ji, and Dong Wang

Doc ID: 270881 Received 21 Jul 2016; Accepted 06 Oct 2016; Posted 10 Oct 2016  View: PDF

Abstract: We here report a design of off-axis three-mirror freeform telescope with a large field of view (FOV) based onintegration mirror (IM). This design is the continuation of authors’ previous work. Based on aberration theory,we established a suitable non-relayed three-mirror-anastigmat (TMA) initial configuration for integrationmirror design. For optical freeform surface, we analyzed the qualitative aberration correction ability of x-ypolynomial surface which can provide a simple convenient and user-friendly relationship between freeformsurface term coefficients and aberrations and then applied the x-y polynomial surface on the tertiary mirror toimprove system optimization degrees of freedom (DOF). In an example with a focal length of 1200 mm, anF-number of 12, and a FOV of 1° × 30°, the tolerance performance was analyzed, and the system presented agood imaging performance. In addition, the IM structure and opto-mechanics support structure were designedand analyzed. The confirmatory design results showed that the integration of the primary mirror and tertiarymirror can improve opto-mechanical properties judged by multiple criteria. In conclusion, the integration ofthe primary mirror and tertiary mirror not only offers alignment convenience as described previously, but alsoimproves system opto-mechanical properties in multiple perspectives. We believe this large linear FOV systembased on IM have broad future applications in optical remote sensing field.

Extended phase matching properties of periodically poled potassium niobate crystals for mid-infrared polarization-entangled photon-pair generation

Kwang Jo Lee, Sunmi Lee, and Heedeuk Shin

Doc ID: 275576 Received 08 Sep 2016; Accepted 06 Oct 2016; Posted 11 Oct 2016  View: PDF

Abstract: We report the extended phase matching (EPM) properties of two kinds of periodically poled potassium niobate (KNbO₃ or KN) crystals (i.e., periodic 180°- and 90°-domain structures) that are highly useful for the generation of polarization-entangled photon-pair in the mid-infrared (IR) spectral region. Under the degenerate Type II spontaneous parametric down-conversion (SPDC) process satisfying the EPM condition, an input single photon with a frequency of 2ω generates a pair of synchronized photons with identical frequencies of ω that are orthogonally polarized with respect to each other, i.e., the frequency-coincident, polarization-entangled bi-photon states. Our simulation results illustrate that the EPM is achievable in the mid-IR spectral region: at the wavelengths of 3.80 μm and 4.03 μm for periodic 90°- and 180°-domain structures, respectively. We will describe in detail the EPM properties of both cases in terms of interaction types and the corresponding nonlinear optic coefficients, phase matching bandwidths, and domain poling periods. The calculated EPM bandwidths are much broader than 200 nm in the mid-IR for both cases, exhibiting a great potential for nonlinear-optic signal processing in quantum communication systems operating in the mid-IR bands.

Fiber Loop Ringdown Humidity Sensor

Chuji Wang and Haifa Alali

Doc ID: 273708 Received 23 Aug 2016; Accepted 06 Oct 2016; Posted 10 Oct 2016  View: PDF

Abstract: A novel optical fiber relative humidity (RH) sensor based on the evanescent field-fiber loop ringdown (EF-FLRD) technique is demonstrated. The sensor was placed inside a chamber that provides a humidity reference which is monitored by a humidity meter. The presence of moisture in the chamber changes the refractive index of the medium; thus the ringdown time changes due to a change in the EF scattering loss induced in the sensor head. The sensor demonstrated a fast response (~ 1 sec), high sensitivity, and excellent reproducibility and reversibly. The EF-FLRD sensor has the capability to measure RH in a wide dynamic range of 4 - 100% at a constant temperature 20 ± 1 °C.

Optical dosimetry probes to validate Monte Carlo andEmpirical-method based NIR dose planning in thebrain

Akshay Prabhu Verleker, Michael Shaffer, Qianqian Fang, Mi-Ran Choi, Susan Clare, and Keith Stantz

Doc ID: 270741 Received 18 Jul 2016; Accepted 05 Oct 2016; Posted 11 Oct 2016  View: PDF

Abstract: A three dimensional photon dosimetry in tissues is critical in designing optical therapeutic protocols to triggerlight activated drug release. The objective of this study is to investigate the feasibility of a Monte Carlo basedoptical therapy planning software by developing dosimetry tools to characterize and cross-validate the localphoton fluence in brain tissue, as part of a long term strategy to quantify the effects of photo-activated drug releasein brain tumors. An existing GPU based 3D Monte Carlo (MC) code was modified to simulate near infrared photontransport with differing laser beam profiles within phantoms of skull bone (B), White Matter (WM) and GrayMatter (GM). A novel titanium based optical dosimetry probe with isotropic acceptance was used to validate thelocal photon fluence, and an empirical model of photon transport was developed to significantly decreaseexecution time for clinical application. Comparisons between the MC and the dosimetry probe measurements wereon an average 11.27%, 13.25%, and 11.81% along the illumination beam axis, and 9.4%, 12.06%, 8.91%perpendicular to the beam axis for WM, GM and B phantoms respectively. For a heterogeneous head phantom, themeasured % errors were 17.71% and 18.04% along and perpendicular to beam axis. The Empirical algorithm wasvalidated by probe measurements and matched the MC results (R2>0.99), with average % error of 10.1%, 45.2%and 22.1% relative to probe measurements; and 22.6%, 35.8% and 21.9% relative to the MC, for WM, GM and Bphantoms respectively. The simulation time for the Empirical model was 6 seconds versus 8 hours for the GPUbased Monte Carlo for a head phantom simulation. These tools provide the capability to develop and optimizetreatment plans for optimal release of pharmaceuticals in the treatment of cancer. Future work will test andvalidate these novel delivery and release mechanisms in vivo.

Application of Picosecond (ps) Laser-Induced Breakdown Spectroscopy (LIBS) to Quantitative Analysis of Boron in Meatballs and Other Biological Samples

Koo Hendrik Kurniawan, Rinda Hedwig, Kurnia Lahna, Zener Lie, Marincan Pardede, May-On Tjia, and Kiichiro Kagawa

Doc ID: 270759 Received 21 Jul 2016; Accepted 05 Oct 2016; Posted 05 Oct 2016  View: PDF

Abstract: This report presents the results of LIBS study on biological and food samples of high water content using ps laser at low output energy of 10 mJ and low pressure helium ambient gas at 2 kPa. Evidence of excellent emission spectra of various analyte elements with very low background are demonstrated for a variety of samples without the need of sample pretreatment. Specifically, limits of detection in the range of sub ppm are obtained for hazardous Pb and B impurities in carrots and meatball. This study also shows the inferior performance of LIBS using ns laser for soft sample of high water content and thereby explain the less successful applications in previous attempts. The present result has instead demonstrated the feasibility of offer LIBS with ps laser and low pressure helium ambient gas as a less costly and more practical alternative for regular high sensitive inspection of harmful food preservatives and environmental pollutants.

Computer generated holograms for fiber opticalcommunication with spatial division multiplexing

Shoam Shwartz, Michael Golub, and Shlomo Ruschin

Doc ID: 272926 Received 01 Aug 2016; Accepted 05 Oct 2016; Posted 05 Oct 2016  View: PDF

Abstract: We report here on applications of computer generated holograms in fiber optical communication with mode-division multiplexing. It is shown that a pair of multichannel spatial filters matched to spatial modes providesviable solution for transmission of several temporal signals of same wavelength in a sole multimode fiber. Spatial filters for combining and decomposition of modes were designed, analyzed , fabricated with diffractive optics technology and optically evaluated.

Multispectral measurement of scattering-angular light distribution in apple skin and flesh samples.

Askoura Mohamed Lamine, Fabrice Vaudelle, and Jean-Pierre L'Huillier

Doc ID: 273891 Received 15 Aug 2016; Accepted 05 Oct 2016; Posted 05 Oct 2016  View: PDF

Abstract: The knowledge of optical properties of apple tissues such as skin and flesh is essential to better understand the light-tissue interaction process and to apply optical methods for apple quality inspection. This work aimed at estimating the anisotropy factor of thin skin and flesh samples extracted from three apple cultivars. The scattering-angular light distribution in each tissue sample was measured at four wavelengths (λ=633, 763, 784 and 852 nm), by means of a goniometer setup. Based on the recorded angular intensity I(θ,λ), the effective anisotropy factor geff of each tissue type was first estimated using the mean statistics applied to the random variable cosθ. Next, the measured data were fitted with three predefined and modified phase functions: Henyey-Greenstein (pMHG), Gegenbauer Kernel (pMGK) and Mie (pMie), in order to retrieve the corresponding anisotropy factors gMHG, gMGK and gMMie. Typically, the anisotropy factors of skin and flesh amount to 0.6-0.8 in the above mentioned wavelengths range.

Relative intersection of confidence intervals rule for sharper restoration of soft x-ray images

Ana Sovic Krzic, Damir Sersic, and Carmen Menoni

Doc ID: 268167 Received 13 Jun 2016; Accepted 05 Oct 2016; Posted 06 Oct 2016  View: PDF

Abstract: We present a novel method for restoration of images of nanostructures obtained with a soft-ray microscope that uses for illumination 46.9 nm soft x-ray laser microscope. To suppress the noise and to preserve the image sharpness, we develop a method based on pixel adaptive zero order modeling of the observed object. Neighboring areas of each pixel are selected using the relative intersection of confidence intervals rule and used for restoration. Due to the non-uniform distribution of noise in the images, we use robust spatial noise modeling. The method provides sharp restored images, when compared to competitive approaches. The sharpness is measured using local phase coherence in the complex wavelet transform domain and shows visible improvement of the novel method.

Stochastic characterization of phase detection algorithms in phase shifting interferometry.

Florin Munteanu

Doc ID: 270922 Received 19 Jul 2016; Accepted 05 Oct 2016; Posted 06 Oct 2016  View: PDF

Abstract: Phase Shifting Interferometry (PSI) is the preferred non-contact method for profiling sub-nanometer surfaces. Based on monochromatic light interference, the method computes the surface profile from a set of interferograms collected at separate stepping positions. Errors in the estimated profile are introduced when these positions are not located correctly. In order to cope with this problem, various algorithms have been developed to minimize the effects of certain types of stepping errors (linear, sinusoidal, etc.). Despite the relatively large number of algorithms suggested in the literature, there is no unified way of characterizing their performance when additional unaccounted errors are present. Here we suggest a procedure for quantifying the expected behavior of each algorithm in the presence of independent and identically distributed (i.i.d.) random stepping errors which occur in addition to the systematic errors for which the algorithm has been designed. The usefulness of this method derives from the fact that it can guide the selection of the best algorithm for specific measurement situations.

A robust air refractometer for accurate compensation of the refractive index or air in everyday use

Oelof Kruger and Naven Chetty

Doc ID: 265034 Received 01 Jun 2016; Accepted 04 Oct 2016; Posted 04 Oct 2016  View: PDF

Abstract: The definition of the metre is based on the speed of light in a vacuum, however, most dimensional measurements, when performed using laser interferometry, are performed in air. A velocity of light compensation needs to be applied to the velocity of the laser light for accurate measurements of the speed of light to be approximated in vacuum. Most practices use a weather station method, whereby the ambient conditions are measured. Thereafter the modified Edlin’s equation is used and corrections are calculated for the wavelength of the laser. The theoretical calculation is however only accurate to 3*10-8 without taking into account the accuracy of the sensors.Thus this work focusses on investigations into the velocity of light compensations both to improve upon the accuracy of the Edlin equation method in everyday use, and to verify the accuracy of the current weather station systems in use through comparison with the refractometer. A refractometer that allows for velocity of light compensation measurements was developed, tested and verified. The system was designed to be simple and cost-effective for use in everyday dimensional measurements but with high accuracy. Achieved results show that although simple in design, the refractometer is accurate to at least 1*10-8 which meets our initial condition for design.

Backplane aberration calibration of spatial light modulators using phase-retrieval algorithm

Xiao Chen, Zhiguang Shi, Xiaotian Chen, Ji Li, and liu wei

Doc ID: 269070 Received 24 Jun 2016; Accepted 04 Oct 2016; Posted 04 Oct 2016  View: PDF

Abstract: The calibration and correction of backplane aberration of a spatial light modulator (SLM) are important for its proper functioning. To simplify the calibration procedurally, we studied a random-illumination-phase-retrieval-based method. Our method improved the convergence of the phase-retrieval-based calibration and reduced the calibration complexity. However, the cross-talk of SLM deteriorates the calibration performance. We determined the relationship between the probability density function (PDF) of the random phases and light-intensity pattern, and proposed an algorithm to compensate for the cross-talk. We conducted a series of simulations to test the performance of the above-mentioned algorithms. The results show that our algorithms are effective and outperform other methods.

3D model of laser treatment by a moving heat sourcewith general distribution of energy in the beam

Zdeněk Veselý, Milan Honner, and Jiří Mach

Doc ID: 269648 Received 30 Jun 2016; Accepted 03 Oct 2016; Posted 04 Oct 2016  View: PDF

Abstract: A three-dimensional model of direct heat treatment of a sample surface with a moving laser has been establishedutilizing the finite element method. Attention is devoted to the preparation of complex boundary conditions of a moving heatsource. Boundary conditions of material heat treatment are defined in the form of the heat transfer coefficient with considerationof several effects. Those include general distribution of energy in the laser beam, laser motion velocity, laser axis position outsidethe sample, and utilization of multiple laser motion tracks over the sample. Various arrangements of sample heat treatment areproposed and computer simulated. Different velocities of laser motion, multiple motion over the same track and simple motionover a number of tracks are investigated. The temperature distribution in the sample and the depths of material heat treatment areevaluated. The simulation model can be used for temperature prediction during laser surface treatment of materials.

Intelligent Estimation of Noise and Blur Variances using ANN for Restoration of Ultrasound Images

Muhammad Uddin, Kalyan Kumar Halder, Murat TAHTALI, Andrew Lambert, Mark Pickering, Margaret Marchese, and Iain Stuart

Doc ID: 268750 Received 29 Sep 2016; Accepted 03 Oct 2016; Posted 04 Oct 2016  View: PDF

Abstract: Ultrasound (US) imaging is a widely used clinical diagnostic tool in medical imaging techniques. It is acomparatively safe, economical, painless, portable, and non-invasive real-time tool compared to the otherimaging modalities. However, the image quality of US imaging is severely affected by the presence of specklenoise and blur during the acquisition process. In order to ensure high quality clinical diagnosis, it requires torestore US images by reducing speckle noise and blur from them. In general, speckle noise is modelled as amultiplicative noise following a Rayleigh distribution and blur as a Gaussian function. Hereto, we propose anintelligent estimator based on artificial neural networks (ANNs) to estimate the variances of noise and blur,which in turn are used to obtain an image without discernible distortions. A set of statistical features computedfrom the image and its complex wavelet sub-bands are used as input to the ANN. In the proposed method, wesolve the inverse Rayleigh function numerically for speckle reduction and use the RichardsonLucy algorithmfor deblurring. The performance of this method is compared with that of the traditional methods by applyingthem to the synthetic, physical phantom and clinical data which confirms better restoration results by theproposed method.

Towards spectral intensity interferometry

Erez Ribak and Georgiy Shoulga

Doc ID: 270885 Received 19 Jul 2016; Accepted 03 Oct 2016; Posted 04 Oct 2016  View: PDF

Abstract: We use intensity interferometry to image a group of point sources, in a computer simulation and laboratory demonstration. We acquire the image of this ‘asterism’ by measuring the second and third order correlations between photon arrival times, using three single photon detectors. To reduce noise effects, we divide the light collector into segments, and each segment is dispersed into spectral bands, where photons in each band are correlated separately. This comprises a new optical design that is (1) stable for partially collimated beams; (2) is light efficient; and (3) is not any wider than the incoming beam.

Energetic material response to ultrafast indirect laser heating

Nhan Dang, Jennifer Gottfried, and Frank De Lucia

Doc ID: 272989 Received 01 Aug 2016; Accepted 03 Oct 2016; Posted 04 Oct 2016  View: PDF

Abstract: The initial evolution of thermal energy transfer into a solid explosive is studied using an indirect laser heating technique on a picosecond timescale in order to elucidate the role of temperature in the shock-induced initiation of explosives. The indirect laser heating method is presented; time-resolved visible transient absorption (TA) spectroscopy was used to monitor the energetic material response following heat transfer from the laser-heated gold (Au) layer to the sample. Reported here are visible TA data in the spectral region from 500 to 750 nm for indirect laser-heated thin films of cyclotrimethylene trinitramine (RDX), oxidized polyethylene (OPE), and RDX with 1, 2.5, 5 or 10% OPE prior to decomposition. TA was observed for RDX and RDX with OPE, however no TA was observed for pure OPE. Compared to pure RDX, the TA intensity of RDX with OPE decreases as the OPE content increases and the time required to observe the TA signal from RDX increases. Our results suggest that the thermal energy couples into RDX molecules via electronic excitation in the excited state and the heat transfer rate in RDX depends on its homogeneity and degree of purity.

Characterization of Grain Sizes and Roughness of HfO2 Single Layers

Xinbin Cheng, Lei Zhang, Jinlong Zhang, Hongfei Jiao, ganghua bao, Tao Ding, and Zhanshan Wang

Doc ID: 274869 Received 30 Aug 2016; Accepted 02 Oct 2016; Posted 04 Oct 2016  View: PDF

Abstract: The grain sizes and their influence on the roughness of HfO2 single layer prepared with ion assisted deposition were investigated. Three methods, X-ray diffractometry, atomic force microscopy and k-correlated power spectral density function model, were used to obtain the grain sizes in a 20nm HfO2 single layer. X-ray diffractometry showed that the grain size was about 9nm, whereas the other two methods demonstrated that the grain sizes were about 16nm. It was thought that X-ray diffractometry underestimated the grain size due to micro strain or shallow penetration depth. The grains in HfO2 single layer leaded to a rough surface which had a significant bulge at middle-high frequency range in power spectral density function curve. The coating intrinsic roughness of HfO2 single layer was separated from the substrate roughness.

Slab-coupled Optical Sensor Fabrication Using Side-Polished Panda Fiber

Rex King, Frederick Seng, Nikola Stan, Kevin Cuzner, Chad Josephson, Stephen Schultz, and Richard Selfridge

Doc ID: 272177 Received 22 Jul 2016; Accepted 02 Oct 2016; Posted 04 Oct 2016  View: PDF

Abstract: A new method of using slab-coupled optical sensor (SCOS) technology was developed to fabricate electric field sensors. This new method replaces the D-fiber used in traditional SCOS technology with side-polished Panda fiber. Panda fiber is cheaper and more easily accessible than the D-fiber previously used and interfaces easier with lab equipment. The fabrication process minimizes the use of Hydrofluoric acid and thus makes the fabrication process much safer. Results show that the Panda sensor achieves results comparable results to the D-fiber sensor and is a suitable replacement.

Cascaded Photonic Crystal Fibers for Three-stage Soliton Compression

Qian Li and Zihao Cheng

Doc ID: 272369 Received 26 Jul 2016; Accepted 02 Oct 2016; Posted 04 Oct 2016  View: PDF

Abstract: Cascaded higher-order soliton compression in PCFs is demonstrated, where both the hyperbolic secant and Gaussian input pulses are considered. Detailed fiber designs for three-stage higher-order soliton compression where soliton order is three or non-integer are presented. A highest compression factor of 219.58 has been achieved with only 51.31% pedestal energy.

Enhanced SAR automatic target recognition method based on novel features

Chen Ning, Wenbo Liu, Gong Zhang, Jiejun Yin, and Xiuxia Ji

Doc ID: 270063 Received 08 Jul 2016; Accepted 02 Oct 2016; Posted 04 Oct 2016  View: PDF

Abstract: This paper proposes a set of uncommonly rich feature representations for automatic target recognition (ATR) in Synthetic Aperture Radar (SAR) images. The proposed novel feature representations capture both the spatial and spectral properties of a target in a unified framework, while simultaneously offering discrimination and robustness to aspect variations. Specifically, the proposed features are mainly derived from the ideas of the monogenic signal and polar mapping. The applicability of the monogenic signal within the field of SAR target recognition is demonstrated by its capability of capturing both the broad spectral information and spatial localization with compact support. Further, to reduce the influence of inevitable variations due to aspect changes in SAR images, the monogenic components are transformed from Cartesian to polar coordinates via polar mapping. Additionally, a new target-shadow feature is also presented to compensate for the important discriminative information about target geometry, which exists in the shadow area. Finally, the proposed features are jointly considered into a unified multiple kernel learning framework for target recognition. Experiments on the moving and stationary target acquisition and recognition (MSTAR) public dataset demonstrate the strength and applicability of the proposed representations to SAR ATR. Moreover, it is also shown that overall high recognition accuracy can be obtained by the established unified framework.

A 3D Model for Rectangular Electrowetting Lens Structures

Zhen Zhang, Collin Hitchcock, and Robert Karlicek

Doc ID: 261428 Received 28 Apr 2016; Accepted 30 Sep 2016; Posted 03 Oct 2016  View: PDF

Abstract: Electrowetting-on-dielectric (EWOD) lens is a good candidate of dynamic beam shaping optics for advanced solid state lighting systems. A geometric approximation model is described to predict the meniscus shape of a rectangular EWOD lens with arbitrary voltages and small Bond numbers. The model approximates the meniscus geometry as being a part of a compound toroidal surface. The model was compared with free energy minimization simulations and experiments with the largest standard deviation between the geometric model and the simulation for a wide variety of bias voltages being less than 2%. The experimental validation compared the measured dynamic image shifts of a wire mesh produced with test EWOD cells with the predicted image obtained from the toroidal geometric model using a ray-tracing simulation. The optical performance of the experimental 3D electrowetting lens is described and was found to agree reasonably well with the predicted optical performance of the geometric model for a wide variety of operating conditions.

Development of Photoacoustic Sensing Platforms at the Army Research Laboratory

Ellen Holthoff and Paul Pellegrino

Doc ID: 272631 Received 01 Aug 2016; Accepted 30 Sep 2016; Posted 03 Oct 2016  View: PDF

Abstract: Traditionally, chemical sensing platforms have been hampered by the opposing concerns of increasing sensor capability while maintaining a minimal package size. Current sensors, although reasonably sized, are geared to more classical chemical threats, and the ability to expand their capabilities to a broader range of emerging threats is uncertain. Recently, photoacoustic spectroscopy, employed in a sensor format, has shown enormous potential to address these ever-changing threats. Photoacoustic spectroscopy is one of the more flexible infrared spectroscopy variants, and that flexibility allows for the construction of sensors that are designed for specific tasks. The Army Research Laboratory has, for the past 14 years, engaged in research into the development of photoacoustic sensing platforms with the goal of sensor miniaturization and the detection of a variety of chemical targets both proximally and at range. This paper reviews this work.

Polarization properties of FEL lamps as applied to radiometric calibration

Kenneth Voss and Leonardo Belmar da Costa

Doc ID: 270926 Received 21 Jul 2016; Accepted 30 Sep 2016; Posted 30 Sep 2016  View: PDF

Abstract: The polarization of the irradiance from several 1000-W FEL lamps was measured between 450 and 900 nm. These lamps are universally used as irradiance calibration standards in radiometric laboratories. The irradiance was polarized between 2.3-3.2%, with the polarization axis aligned with the coiled filament, nearly perpendicular to the lamp axis. A simple model of the filament is presented that explains the degree of polarization and the plane of polarization, based on the polarized emissivity of tungsten, and gives an approximate value for this polarization. While the irradiance is polarized, this polarization does not significantly effect the polarization of the light when reflected from a Spectralon plaque (Labsphere, Inc.). The polarization of these lamps should be taken into account when using these FEL lamps to characterize optical instruments, particularly grating spectrometers without polarization scrambling devices.

Wavelength tuning in cryogenically-cooled lasers based on Er-doped orthovanadates

Nikolay Ter-Gabrielyan and Viktor Fromzel

Doc ID: 273083 Received 02 Aug 2016; Accepted 28 Sep 2016; Posted 30 Sep 2016  View: PDF

Abstract: Continuous tuning between 1590 nm and 1612 nm has been demonstrated in cryogenically cooled lasers with composite active media constituting of Er:YVO4, Er:LuVO4 and Er:GdVO4 crystals resonantly pumped by a fiber coupled laser diode emitting at 1529 nm. Wavelength tuning was implemented using intracavity single-plate birefringent filter.

Threshold secret sharing scheme based onphase-shifting interferometry

Xiaopeng Deng, Zhengang Shi, and wei wen

Doc ID: 273346 Received 08 Aug 2016; Accepted 28 Sep 2016; Posted 30 Sep 2016  View: PDF

Abstract: We propose a new method for secret image sharing with the (3,N)threshold scheme based on phase-shifting interferometry. The secret image, which ismultiplied with an encryption key in advance, is firstly encrypted by using Fouriertransformation. Then, the encoded image is shared into N shadow images based onrecording principle of phase-shifting interferometry. Based on reconstruction principleof phase-shifting interferometry, any three or more shadow images can retrieve thesecret image, while any two or fewer shadow images can not obtain any informationof the secret image. Thus, a (3,N) threshold secret sharing scheme can beimplemented. Compared with our previously reported method, the algorithm of thispaper is suited for not only binary image but also grayscale image. Moreover, theproposed algorithm can obtain a larger threshold value t . Simulation results arepresented to demonstrate the feasibility of the proposed method.

Tchebichef Moment based Restoration of Gaussian Blurred Images

Ahlad Kumar, Raveendran Paramesran, Chern Lim, and Sarat Dass

Doc ID: 272263 Received 22 Jul 2016; Accepted 28 Sep 2016; Posted 30 Sep 2016  View: PDF

Abstract: With the knowledge of how edges vary in the presence of the Gaussian blur, a method that uses low order Tchebichef moments is proposed to estimate the blur parameters: sigma (σ) and size (w). The difference of the Tchebichef moments of the original and the reblurred images are used as feature vectors to train extreme learning machine (ELM) for estimating the blur parameters (σ, w) respectively. The effectiveness of the proposed method to estimate the blur parameters is examined using cross database validation. The estimated blur parameters from the proposed method are used in the split Bregman based image restoration algorithm. A comparative analysis of the proposed method with three existing methods using all the images from the LIVE database is carried out. The results show that the proposed method in most of the cases performs better than the three existing methods in terms of the visual quality evaluated using structural similarity (SSIM) index.

Quantification of optical turbulence in the ocean and its effects on beam propagation

Gero Nootz, Weilin Hou, Fraser Dalgleish, and Ewa Jarosz

Doc ID: 269405 Received 06 Jul 2016; Accepted 28 Sep 2016; Posted 30 Sep 2016  View: PDF

Abstract: The influence of optically active turbulence on the propagation of laser beams is investigated in clear ocean water over a path length of 8.75m. The measurement apparatus is described and the effects of optical turbulence on the laser beam are presented. The index of refraction structure constant is extracted from the beam deflection and the results are compared to independently made measures of the turbulence strength by a vertical microstructure profiler. Here we present values of C_n^2 taken from aboard the R/V Walton Smith during the Bahamas Optical Turbulence Exercise (BOTEX) in the Tongue of the Ocean between June 30 and July 12, 2011, spanning a range from 10-14 to 10-10 m-2/3. To the best of our knowledge, this is the first time such measurements are reported for the ocean.

The estimation of GSSM calibration error

Han Linchu, zhang jingxu, Fei Yang, and Qichang An

Doc ID: 269717 Received 01 Jul 2016; Accepted 27 Sep 2016; Posted 30 Sep 2016  View: PDF

Abstract: The calibration of the tertiary mirror of the Thirty Meter Telescope, also known as the Giant Science SteeringMirror (GSSM), is a step of great significance during its testing process. Systematic, drift, and random errorsconstitute the major limitations to the accuracy of the calibration measurements. In this article, we estimated theerrors in the calibration of the GSSM with a laser tracker. For the systematic error, a measurement strategy basedon the standard bar method was successfully designed and applied. At the same time, we can distinguish betweenthe drift and random errors by means of a correlation analysis. The systematic error, which depends strongly onthe configuration of the system formed by the GSSM and the laser tracker, was estimated to be 20 μm for the GSSMprototype. The random error, averaging 15 min, was about 4 μm. The correlation coefficients among threedifferent noise measurements are all lower than 0.1, which indicates that the noise is dominated by random errors.Finally, the error can be sufficiently suppressed by rearranging the position of the spherically mountedretroreflectors (SMRs). The result shows that the accuracy of the measurement can be improved by 21.4% with thenew arrangement method.

Ultra-Low Refractive Index Optical Films with Enhanced Mechanical Performance Obtained by Hybrid Glancing Angle Deposition

William Trottier-Lapointe, Oleg Zabeida, Thomas Schmitt, and Ludvik Martinu

Doc ID: 273059 Received 03 Aug 2016; Accepted 27 Sep 2016; Posted 27 Sep 2016  View: PDF

Abstract: Ultra-low refractive index materials (n less than 1.38 @ 550nm) are of particular interest in the context of anti-reflective coatings allowing one to enhance their overall optical performance. However, application of such materials is typically limited by their mechanical properties. In this study, we explore the characteristics of a new category of hybrid (organic/inorganic) SiOCH thin films prepared by glancing angle deposition (GLAD) using electron beam evaporation of SiO2, in the presence of an organo-silicone precursor. The resulting layers exhibited n as low as 1.2, they showed high elastic rebound and generally better mechanical properties than their inorganic counterparts. In addition, hybrid GLAD films were found to be highly hydrophobic. The performance of the films is discussed in terms of their hybridicity (organic/inorganic) ratio determined by infrared spectroscopic ellipsometry, as well as the presence of anisotropy assessed by the nanostructure-based spectroscopic ellipsometry model. Finally, we demonstrate successful implementation of the ultra-low index material in a complete antireflective stack.

Effect of background pressure on Co/C multilayers

Mingwu Wen, Shuang Ma, Qiushi Huang, Li Jiang, Pin Li, Zhong Zhang, Zhanshan Wang, Delai Wang, and Mingqi Cui

Doc ID: 275057 Received 02 Sep 2016; Accepted 27 Sep 2016; Posted 27 Sep 2016  View: PDF

Abstract: Co/C multilayers with period thickness of 3.54 nm and bi-layer number of 30 were deposited by direct current magnetron sputtering with different background pressure. The effects of residual background air were investigated. The films were characterized by using grazing incidence hard X-ray reflectivity, soft X-ray reflectivity and X-ray photoelectron spectroscopy. The results indicate that the X-ray reflectivity of Co/C multilayers decreases with increasing background pressure as well as the increasing interlayer roughness. The inclusion of more residual background air increases the inter-diffusion of Co and C layers.

Intermixing studies in GaN1−xSbx highly mismatched alloys

Wendy Sarney, Stefan Svensson, Min ting, Natalie Segercrantz, W. Walukiewicz, Kin Man Yu, Robert Martin, Sergei Novikov, and C.T Foxon

Doc ID: 270357 Received 12 Jul 2016; Accepted 27 Sep 2016; Posted 29 Sep 2016  View: PDF

Abstract: GaN1−xSbx with x~ 5-7% is a highly mismatched alloy predicted to have favorable properties for application as an electrode in a photo-electrochemical cell for solar water splitting. In this study, we grew GaN1−xSbx under conditions that were intended to induce phase segregation. Prior experiments with GaN1−xAsx, the tendency of Sb to surfact, and the low growth temperatures needed to incorporate Sb all suggested that GaN1−xSbx alloys would likely exhibit phase segregation. We found that, except for very high Sb compositions, this was not the case and that instead interdiffusion dominated. Characteristics measured by optical absorption were similar to intentionally grown bulk alloys for the same composition. Furthermore, the alloys produced by this method maintained crystallinity for very high Sb compositions, and allowed higher overall Sb compositions. This method may allow higher temperature growth while still achieving needed Sb compositions for solar water splitting applications.

Simulation and experimental verification for imaging of grayscale objects through scattering layers

Huijuan Li, Tengfei Wu, jietao liu, changmei gong, and Xiaopeng Shao

Doc ID: 272008 Received 20 Jul 2016; Accepted 27 Sep 2016; Posted 29 Sep 2016  View: PDF

Abstract: We analyze the imaging of grayscale object through highly scattering layers. The theoretical investigation with numerical simulations shows that contrast of the speckle autocorrelations varies regularly with the change of the grayscale of the object. Therefore, gray information is well contained in the autocorrelations of the speckle patterns, and grayscale objects are able to be exacted from these autocorrelations via speckle correlation technology. Combined with phase retrieval via generalized approximate message passing algorithm, recovery of the objects is realized and accurate grayscale reconstruction is demonstrated via numerical simulations. Experiment results further demonstrate the good performance of the scheme in imaging of grayscale objects through scattering layers. Particularly, this work will be benefit to applications of imaging through turbid medium in biomedical and bio-photonics imaging.

Scintillations of LED sources in oceanic turbulence

Yahya Baykal

Doc ID: 272516 Received 26 Jul 2016; Accepted 27 Sep 2016; Posted 30 Sep 2016  View: PDF

Abstract: The scintillation index of light emitting diode (LED) sources is evaluated when such sources are employed in oceanic wireless opticalcommunication (UWOC) links. In the formulation, LED source radiation is taken to be perfectly incoherent with a Gaussian fielddistribution. We have utilized the scintillation index solution of an incoherent source in atmospheric turbulence, together with ourrecently obtained expression that expresses the structure constant of atmospheric turbulence in terms of the oceanic turbulence andUWOC link parameters. Oceanic turbulence parameters of interest are the ratio of temperature to salinity contributions to the refractiveindex spectrum, rate of dissipation of kinetic energy per unit mass of fluid, rate of dissipation of mean-squared temperature andviscosity. UWOC link parameters are the LED source size, link length and the wavelength. Scintillation index results are presented forvarious variations of the oceanic turbulence and UWOC link parameters.

Radial distortion correction in a vision system

Qiyue Wang, Tim Smith, and wang zhongyu

Doc ID: 272533 Received 27 Jul 2016; Accepted 27 Sep 2016; Posted 30 Sep 2016  View: PDF

Abstract: Accurate correction of lens distortion is the core technology in visual based measurements. Radial distortion is themost significant lens distortion in vision system. In this paper a radial distortion correction method namediteration geometrical similar method is proposed. The initial method is used to obtain geometrical similar degreeof image points. The distortion coefficients are then estimated by using iteration approximation model. The radialdistortion coefficients and other camera parameters can be successfully decoupled. Both simulative and practicalexperiments have been carried out to evaluate the performance of the proposed method. Firstly, the influence ofimage noise and distortion degree on correction results is discussed in computer simulations. The results showthat correction performance of proposed method is manifested well. At meantime the proposed method comparedwith linear regression analysis (LRA) and diversion model (DM) in the practical experiment. The results indicatethat the average straightness calculated by proposed method is only 0.195pixels, compared with 0.394 pixels and0.438 pixels by LRA and DM respectively. At the meantime, the rectified images are used to calibrate the camera.The mean reprojection error using rectified images corrected by proposed method is only 0.137 pixels, which issignificant less than 0.421 pixels and 0.462 pixels by the LRA and DM respectively.

Simplified expression for estimating the nonlinear refractive index of typical optical coating materials

Olaf Stenzel

Doc ID: 272625 Received 28 Jul 2016; Accepted 27 Sep 2016; Posted 30 Sep 2016  View: PDF

Abstract: A semiempirical equation is derived that allows estimating the electronic contribution to the nonlinear refractive index of an optical material from knowledge of the linear one. The approach is restricted to practically loss-free media at low frequencies. In contrast to other approaches, no explicit data on the optical gap or Abbe number are required. A comparison with experimental data from typical oxide and fluoride materials reveals an excellent agreement between experiment and theoretical estimation.

Random lasing from cholesteric liquid crystal microspheres dispersed in glycerol

Dan Luo, Yong Li, and Rui Chen

Doc ID: 272252 Received 22 Jul 2016; Accepted 27 Sep 2016; Posted 30 Sep 2016  View: PDF

Abstract: We demonstrate random lasing from a scattering system formed by cholesteric liquid crystal dispersed in glycerol. Strongly scattering of light is produced from the interference between cholesteric liquid crystal microsphere and glycerol and leads to the random lasing. The optical properties of random lasing, such as intensity, threshold and the temperature effect on lasing emission are demonstrated. The random laser is distinguished from the band-edge laser generated within cholesteric liquid crystal microspheres by analyzing the positions of photonic band-edge of cholesteric liquid crystal and photoluminescence of doped laser dye. The random laser from CLC microspheres in glycerol possesses simple fabrication process, small volume, and low threshold, which enable it to be used in speckle-free imaging, target identification, biomedicine, document coding, and other photonic devices.

Characterization of slow dynamics in turbidcolloidal systems by a cross-correlation schemebased on echo dynamic light scattering

Luis Rojas-Ochoa, Angel Zuccolotto-Bernez, Nasser Ben Braham, and Catalina Haro-Perez

Doc ID: 269588 Received 30 Jun 2016; Accepted 27 Sep 2016; Posted 03 Oct 2016  View: PDF

Abstract: We describe the implementation of echo dynamic light scattering in a cross-correlation detection scheme that enables the study of slow dynamics in moderately turbid colloidal systems by adapting a commercial light scattering device. Our setup combines the three-dimensional cross-correlation detection scheme (3DDLS), which allows for suppression of multiple scattering, with the speckle echo technique for dynamic light scattering. The recorded cross-correlation echoes provide precise ensemble-averaged results that appropriately describe sample dynamics of ergodic and non-ergodic colloidal systems of different turbidities. Additionally, the high mechanical stability achieved in our setup makes possible an absolute estimation of the scattering intensity correlation function (ICF) directly from the height of echoes thus making unnecessary any correction for imperfect rotation of the sample or of any ad-hoc assumption regarding the correspondence between the absolute values of echoes height and ICF. Furthermore, we find that zeroth order echo height represents the coherence factor of the 3DDLS experiment.

Determining the Refractive Index of Human Hemoglobin Solutions by Kramers-Kronig Relations with an Improved Absorption Model

Jonas Gienger, Hermann Gross, Joerg Neukammer, and Markus Baer

Doc ID: 272064 Received 22 Jul 2016; Accepted 27 Sep 2016; Posted 07 Oct 2016  View: PDF

Abstract: The real part of the refractive index (RI) of aqueous solutions of human hemoglobin is computed from their absorption spectra in the wavelength range 250nm–1100nm using the Kramers-Kronig (KK) relations and the corresponding uncertainty analysis is provided. The strong ultraviolet (UV) and infrared absorbance of the water outside this spectral range were taken into account in a previous study employing KK relations. We improve these results by including the concentration dependence of the water absorbance as well as by modeling the deep UV absorbance of hemoglobin’s peptide backbone. The two free parameters of the model for the deep UV absorbance are fixed by a global fit.

Enhanced absorptance of the assembly structureincorporating germanium nanorods and twodimensionalsilicon gratings for photovoltaics

Qiang Cheng, Zhihao Jia, Jinlin Song, Yifan Zhou, and Yang Liu

Doc ID: 270384 Received 11 Jul 2016; Accepted 26 Sep 2016; Posted 27 Sep 2016  View: PDF

Abstract: This paper proposes an assembly structure incorporating two-dimensional silicon gratings and germaniumnanorods applied to photovoltaic absorbers. The absorptance of assembly structure is numerically investigatedusing the finite-difference time-domain (FDTD) method. The results demonstrate that such structure can greatlyimprove the absorptance and conversion efficiency compared with gratings or nanowires in the 300 – 1100 nmwavelength region. And the average spectral absorptance of such structure reaches up to 0.983, even closes tounity in some wave regions, which is mainly attributed to guided mode resonance and Fabry-Perot resonanceidentified by analyzing the electromagnetic field and power dissipation. The effects of different diameters andlengths of the nanorod component, as well as the widths and depths of the grating component, on the absorptanceare further examined. It is found that the absorptance of assembly structure is insensitive to the incident angle lessthan 30° for both TM and TE waves. The photovoltaic absorbers with such structure can yield ideal conversionefficiency as high as 47.9%, which shows great potential for applying the assembly structure to photovoltaicabsorbers.

Study on Fatigue Damage Characteristics of Deformable Mirrors under Thermal-mechanical Coupling Effect

Bin Zhang, LIxia Chen, Zhen Wu, and Nian-Chun Sun

Doc ID: 272404 Received 26 Jul 2016; Accepted 25 Sep 2016; Posted 27 Sep 2016  View: PDF

Abstract: In a wavefront correction process, both the mechanical effect and the irradiation of high power continue wave(CW) laser distort the deformable mirror (DM) surface, which inevitably speed up the fatigue damage of the DM. Byutilizing the stress analysis model for the fatigue damage of the DM, the fatigue damage effects are analyzedquantitatively on the consideration of thermal-mechanical coupling effects, and the fatigue life prediction modelhas further been proposed based on the S-N curve and Miner cumulative damage theory. On this basis, thermalmechanicalconditions have been analyzed, and the influence of laser parameters on the fatigue life of the DM hasalso been discussed in detail. The results indicate that the increasing of maximum temperature rise of the DM leadsto the increasing of stress, and further brings about the decreasing of the fatigue life. Meanwhile, the position at therear surface of the DM subjected the maximum stress always presents the minimum fatigue life. Furthermore, thelaser irradiation makes the DM more easily be damaged when the DM is correcting a distorted wavefront, and thefatigue life decreases with the increasing of irradiation time and power density for a given PV value of thecorrected wavefront. Additionally, the fatigue life also decreases with the increasing of power density and thedecreasing of spot radius for a certain total irradiation. On the other hand, for the given laser parameters, theinfluence of the mechanical effect on fatigue life is gradually apparent with increasing PV value of the correctedwavefront, and when the PV value is more than 2λ, the mechanical effect instead of the thermal effect becomes thekey factor for fatigue damage of the DM.

Fundamental uncertainty limit of optical flow velocimetry according to Heisenberg's uncertainty principle

Andreas Fischer

Doc ID: 273478 Received 09 Aug 2016; Accepted 25 Sep 2016; Posted 27 Sep 2016  View: PDF

Abstract: Optical flow velocity measurements are important for understanding the complex behavior of flows. Although a huge variety of methods exists, theyare either based on a Doppler or a time-of-flight measurementprinciple. Doppler velocimetry evaluates the velocity dependent frequencyshift of light scattered at a moving particle, whereas time-of-flightvelocimetry evaluates the travelled distance of a scattering particle per time interval. Regarding the aim of achieving a minimal measurementuncertainty, it is unclear if one principle allows to achieve loweruncertainties or if both principles can achieve equal uncertainties. Forthis reason, the natural, fundamental uncertainty limit according toHeisenberg's uncertainty principle is derived for Doppler and time-of-flightmeasurement principles, respectively. The obtained limits of the velocityuncertainty are qualitatively identical showing e.\,g. a directproportionality for the absolute value of the velocity to the power of3/2 and an indirect proportionality to the square root of thescattered light power. Hence, both measurement principles have identicalpotentials regarding the fundamental uncertainty limit due to the quantummechanical behavior of photons. This fundamental limit can be attained (atleast asymptotically) in reality either with Doppler or time-of-flightmethods, because the respective Cramér-Rao bounds for dominating photon shot noise, which is modeled as white Poissonian noise, are identical with the conclusions from Heisenberg's uncertainty principle.

Characterization of commercially-available vertical-cavity surface emitting lasers tuned on Cs D1 line at 894.6 nm for miniature atomic clocks

Eric Kroemer, Jaroslaw Rutkowski, Vincent Maurice, Remy Vicarini, Moustafa Abdel Hafiz, Christophe Gorecki, and Rodolphe Boudot

Doc ID: 269295 Received 27 Jun 2016; Accepted 25 Sep 2016; Posted 03 Oct 2016  View: PDF

Abstract: We report on the metrological characterization of newly commercially-available 894.6 nm vertical-cavity surface-emitting lasers(VCSELs), dedicated to Cs D1 line spectroscopy experiments. The dc current-to-optical power dependence and the temperature-to-power dependence are measured. The laser relative intensity noise (RIN) is measured to be -118 dB/Hz at 100 Hz Fourier frequency, for a laser power of 25 uW and found to be reduced with increased power. The VCSEL frequency noise is 10^{10} f^{-1} Hz^2/Hz in the 1 Hz - 100 Hz Fourier frequency range. The typical optical linewidth of the VCSEL is about 30 MHz. Direct modulation at 4.596 GHz of the VCSEL injection current was performed with microwave powers in the range of -10 to +0 dBm to generate optical sidebands. The VCSEL was used as the laser source of a Cs atomic clock based on coherent population trapping (CPT). The detection of a typical CPT clock resonance signal with a linewidth of 8 kHz and a contrast of 2 % in a Ne buffer gas-filled micro-fabricated Cs cell is reported. A CPT clock short-term fractional frequency instability of 4 10^{-11} \tau^{-1/2} up to about 10 s is reported, proving the potential of these VCSEL diodes for miniature atomic clocks applications.

Thermography and Machine Learning Techniques forTomato Freshness Prediction

Sheng-Jen Hsieh, Jing Xie, Hongjin Wang, and Zuojun Tan

Doc ID: 269687 Received 01 Jul 2016; Accepted 24 Sep 2016; Posted 27 Sep 2016  View: PDF

Abstract: The United States and China are the world’s leading tomato producers. Tomatoes account for over $2 billion annually in farm sales in the U.S.Tomatoes also rank as the world’s 8th most valuable agricultural product, valued at $58 billion dollars annually, and quality is highly prized. Nondestructivetechnologies, such as optical inspection and near infrared spectrum analysis, have been developed to estimate tomato freshness(also known as grades in USDA parlance). However, determining the freshness of tomatoes is still an open problem. This research (1) illustratethe principle of theory on why thermography might be able to reveal the internal state of the tomatoes and (2) investigated the application ofmachine learning techniques—Artificial Neural Networks (ANN) and Support Vector Machines (SVM)—in combination with transient stepheating, and thermography for freshness prediction, which refers to how soon the tomatoes will decay. Infrared images were captured at asampling frequency of 1 Hz during 40-seconds of heating following by 160 seconds of cooling. The temperatures of the acquired images wereplotted. Regions with higher temperature differences between fresh and less fresh (rotten within three days) tomatoes of approximatelyuniform size and shape were used as the input nodes for ANN and SVM models. The ANN model built using heating and cooling data wasrelatively optimal. The overall regression coefficient was 0.99. These results suggest that a combination of infrared thermal imaging and ANNmodeling methods can be used to predict tomato freshness with higher accuracy than SVM models.

Broadband and highly absorbing multilayer structure in mid-infrared

Zhijun Liu, Hao Peng, Yi Luo, Xiangxiao Ying, Yang Pu, Yadong Jiang, and Jimmy Xu

Doc ID: 269455 Received 30 Jun 2016; Accepted 22 Sep 2016; Posted 30 Sep 2016  View: PDF

Abstract: In this paper, we have designed and experimentally demonstrated a broadband absorber in the mid-infrared region based on the impedance matching method. The absorber is made of planar multilayered dielectric and metallic films without involving lithography in fabrication. Our measurements reveal high absorption over 85 % in the wavelength range of 2.2 μm to 6.2 μm. This wideband absorption is shown to be independent of the polarization, and can be maintained over a range of incident angles up to 45 °. The resultant absorber has potential applications for thermal shielding, camouflaging and sensing etc.

Wavefront sensing by numerical evaluation ofdiffracted wavefields

Mohamed Bichra, Nail Sabitov, Thomas Meinecke, and Stefan Sinzinger

Doc ID: 273180 Received 04 Aug 2016; Accepted 22 Sep 2016; Posted 23 Sep 2016  View: PDF

Abstract: A novel wavefront sensor principle based on diffraction theory and Fourier analysis with a modifiedangular spectrum propagator has been developed. We observe the propagation of a wavefront behind atwo-dimensional cross grating and derive a universal method to extract the phase gradient directly froma captured intensity image. To this end the intensity distribution is analyzed in the spectral domain andthe processing is simplified by an appropriate decomposition of the propagator kernel. This methodworks for arbitrary distances behind the grating. Our new formulation is verified through simulations.The wavefront generated by a freeform surface is measured by the new method and compared withmeasurements from a commercial Shack- Hartmann wavefront sensor.

New Materials Design Parameters for Infrared Device Applications

Stefan Svensson, Wendy Sarney, DMITRY DONETSKY, GELA KIPSHIDZE, YOUXI LIN, Leon Shterengas, YE XU, and Gregory Belenky

Doc ID: 270450 Received 12 Jul 2016; Accepted 22 Sep 2016; Posted 26 Sep 2016  View: PDF

Abstract: The collaborative development of infrared detector materials by the Army Research Laboratory (ARL) and Stony Brook University has led to new fundamental understandings of materials, as well as new levels of control and flexibility in III-V semiconductor crystal growth by molecular beam epitaxy. Early work on mid-wave strained layer superlattice (SLS) cameras led to a subsequent focus on minority carrier lifetime studies, which resulted in the proposal of the Ga-free SLS on GaSb substrates. The later demonstration of virtual substrate technology allowed the lattice constant to become a design parameter and enabled growth of undistorted bulk InAsSb. When grown in that manner, InAsSb has a bandgap bowing parameter large enough to cover absorption wavelengths across the entire long-wavelength band (8-12 micron). Even longer wavelengths are achieved with a general Ga-free SLS approach, with a virtual substrate having a lattice constant significantly larger than that of GaSb, and with InAsSb in both bi-layers in the period. Since these layers can also be made very thin, the general Ga-free SLS does not suffer from the relatively low optical absorption and poor hole transport, which is characteristic of the special Ga-free SLS on GaSb for long-wavelength designs. Finally, the general Ga-free InAsSb SLS provides a method to induce and control sustained atomic ordering, which is yet another new design parameter.

Thermography for skin temperature evaluation during dynamics exercise, a study case on an incremental maximal test in elite male cyclists

nicola ludwig, athos trecroci, marco gargano, damiano formenti, andrea bosio, ermanno rampinini, and giampiero alberti

Doc ID: 270699 Received 15 Jul 2016; Accepted 21 Sep 2016; Posted 23 Sep 2016  View: PDF

Abstract: The use of thermal imaging in monitoring the dynamic of skin temperature during a prolonged physical exercise iscentral to assess the athletes’ ability to dissipate heat from the skin surface to the environment. In this study, seven elitecyclists completed an incremental maximal cycling test to evaluate their skin temperature response under controlledenvironmentconditions. Thermal images have been analyzed using a method based on maxima detection (Tmax). Dataconfirmed a reduction in skin temperature due to vasoconstriction during the exercise followed by a temperatureincrement after the exhaustion. A characteristic hot-spotted thermal pattern was found over the skin surface in allsubjects. This research confirmed also the notable ability by highly trained cyclists to modify skin temperature duringan incremental muscular effort. This study gives additional contributions in the understanding the capability of Tmaxmethod applied to thermoregulation and physiological processes.

Laser-shocked energetic materials with metal additives: evaluation of chemistry and detonation performance

Jennifer Gottfried and Eric Bukowski

Doc ID: 272827 Received 01 Aug 2016; Accepted 21 Sep 2016; Posted 23 Sep 2016  View: PDF

Abstract: A focused, nanosecond-pulsed laser has been used to ablate, atomize, ionize, and excite milligram quantities of metal-doped energetic materials which undergo exothermic reactions in the laser-induced plasma. The subsequent shock wave expansion in the air above the sample has been monitored using high-speed schlieren imaging in a recently developed technique, laser-induced air shock from energetic materials (LASEM). The method enables the estimation of detonation velocities based on the measured laser-induced air-shock velocities, and has previously been demonstrated for organic military explosives. Here, the LASEM technique has been extended to explosive formulations with metal additives. A comparison of the measured laser-induced air-shock velocities for TNT, RDX, DNTF, and LLM-172 doped with Al or B to the detonation velocities predicted by the thermochemical code CHEETAH for inert or active metal participation demonstrates that LASEM has potential for predicting the early time (<10 μs) participation of metal additives in detonation events. The LASEM results show that while Al is mostly inert at early times in the detonation event (confirmed from large-scale detonation testing), B is active – and reducing the amount of hydrogen present during the early chemical reactions increases the resulting estimated detonation velocities.


Detlef Mueller, Alexei Kolgotin, Eduard Chemyakin, and Anton Romanov

Doc ID: 266604 Received 29 Aug 2016; Accepted 12 Sep 2016; Posted 14 Sep 2016  View: PDF

Abstract: Mutliwavelength Raman/high-spectral-resolution lidars that measure backscatter coefficients at 355, 532, and 1064 nm and extinction coefficients at 355 and 532 nm can be used for the retrieval of particle microphysical parameters such as effective and mean radius, number, surface-area and volume concentrations, and complex refractive index from inversion algorithms. In this study we investigate correlation properties that may exist between the optical properties measured with these lidars and the underlying microphysical properties. Goal of the study is if results from data inversion can be improved, or if data inversion can even be replaced with simpler schemes if such correlation properties are used in the inversion in terms of a-priori or a-posteriori constraints. We made the simplifying assumption of error-free optical data in order to find out what correlation in the best case situation would exist. Clearly, for practical applications, erroneous data need to be considered, too. On the basis of simulations with synthetic optical data we find the following results which hold true for arbitrary particle size distributions, i.e., regardless of the modality or the shape of the size distribution function: surface-area concentrations and ex-tinction coefficients are linearly correlated with a correlation coefficient above 0.99. We also find a correlation coefficient above 0.99 for the extinction coefficient versus (1) the ratio of the volume concentration to effective radius and (2) the product of number concentration times the sum of the squares of mean radius and standard deviation of the investigated particle size distributions. Besides that we find that for particles of any mode fraction of the particle size distribution the complex refractive index is uniquely defined by extinction- and backscatter-related Ångström exponents, lidar ratios at two wavelengths and effective radius.


Detlef Mueller, Alexei Kolgotin, Eduard Chemyakin, and Anton Romanov

Doc ID: 266606 Received 29 Aug 2016; Accepted 12 Sep 2016; Posted 14 Sep 2016  View: PDF

Abstract: We developed a mathematical scheme that allows us to improve retrieval products obtained from the inversion of multiwavelength Raman/HSRL lidar data, commonly dubbed “3 backscatter + 2 extinction” (3β+2α) lidar. This scheme works independently of our automated inversion method that we currently develop in the framework of the ACE (Aerosol-Cloud-Ecosystem) mission and which is successfully applied since 2012 to data collected with the first airborne multiwavelength 3β+2α HSRL, developed at NASA Langley Research Center. The mathematical scheme uses gradient correlation relationships we presented in part 1 of our study in which we investigated lidar data products and particle microphysical parameters from one and the same set of optical lidar profiles. For an accurate assessment of regression coefficients that are used in the correlation relationships we specially designed the proximate analysis method that allows us to search for a first-estimate solution space of particle microphysical parameters on the basis of a look-up table. The scheme works for any shape of particle size distribution. Simulation studies demonstrate a significant stabilization of the various solution spaces of the investigated aerosol microphysical data products if we apply this gradient correlation method in our traditional regularization technique. Surface-area concentration can be estimated with an uncertainty that is not worse than the measurement error of the underlying extinction coefficients. The retrieval uncertainty of effective radius is as large as +-0.07 mu for fine mode particles and approximately 100 % for particle size distributions composed of fine (submicron) and coarse (supermicron) mode particles. Volume concentration uncertainty is defined by the sum of the uncertainty of surface-area concentration and the uncertainty of effective radius. The uncertainty of number concentration is better than 100% for any radius domain between 0.03 and 10 mu. For monomodal PSDs the uncertainties of the real and imaginary parts of the CRI can be restricted to +-0.1 and +-0.01 on the domains [1.3; 1.8] and [0; 0.1], respectively.

Dependence of depth of focus on spherical aberration of optical systems

Antonin Miks and Jiri Novak

Doc ID: 267338 Received 31 May 2016; Accepted 05 Jul 2016; Posted 06 Jul 2016  View: PDF

Abstract: This paper presents a theoretical analysis and computation of aberration coefficients of the third and fifth order of transverse spherical aberration of an optical system, which generates a ray bundle with a diameter of a geometric-optical circle of confusion smaller than a predetermined limit value. Equations were derived for the calculation of aberration coefficients of an optical system, which satisfy given conditions, and for the determination of the maximum possible depth of focus for given conditions.

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