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Accepted papers to appear in an upcoming issue

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Narrow-linewidth broadly tunable Yb-doped Q-switched fiber laser using multimode interference filter

Usha Chakravarty, Pranab Mukhopadhyay, Antony Kuruvilla, B. N. Upadhyaya, and kushvinder Bindra

Doc ID: 282823 Received 15 Dec 2016; Accepted 24 Mar 2017; Posted 24 Mar 2017  View: PDF

Abstract: Narrow linewidth broadly tunable Q-switched Yb-doped fiber laser using acousto-optic modulator (AOM) and multimode interference filter (MMIF) in the linear bulk cavity resonator and all fiber ring cavity resonator has been demonstrated. Insertion of MMIF in the linear cavity resonator using bulk components decreased the spectral bandwidth of the Q-switched signal by two orders of magnitude from 11 nm to less than 0.1 nm. Spectral tunability of more than 16 nm, in the range from 1057 nm to 1073 nm, has also been achieved by the combination of MMIF and a standard polarization controller (SPC). Decrease in the pulse duration with decrease in the spectral bandwidth of the output signal has also been recorded. The pulse duration of Q-switched signal reduced from ~305 ns to ~240 ns by the introduction of the MMIF in the resonator at the same value of the input pump power. In the case of all fiber Q-switched ring cavity resonator the spectral bandwidth of the Q-switched signal reduced by two orders of magnitude from ~17 nm to less than 0.1 nm due to the introduction of MMIF in the resonator. The spectral tunability of more than 12 nm, in the range from 1038 nm to 1050 nm was achieved by MMIF and a SPC.

Spectral shaping for suppressing Stimulated-Raman-Scattering in fiber laser

Haiyang Xu, Man Jiang, Chen Shi, Pu Zhou, Guomin Zhao, and Xijia Gu

Doc ID: 283539 Received 23 Dec 2016; Accepted 24 Mar 2017; Posted 24 Mar 2017  View: PDF

Abstract: We report the effects of spectral shaping of the output coupler fiber Bragg grating (OC-FBG) in a Yb-doped fiber laser on the laser emission spectrum for the purpose of inhabiting Stimulated Raman Scattering (SRS). The lasers with four different OC-FBGs were built and characterized. We found that the laser with a chirped-moiré OC-FBG with multiple reflection peaks produced a broad laser emission linewidth, which in turn, led to about 100 times lower SRS emission as compared to the laser with a 0.19 nm Gaussian-shaped OC-FBG. A nearly top-flat laser output spectrum was obtained from the lasers with a triangle-shaped and chirped-moiré OC-FBG respectively.

Accurate determination of dielectric permittivity of polymers from 75 GHz to 1.6 THz using both S-parameters and transmission spectroscopy

Tianying Chang, xiansheng zhang, Xiaoxuan Zhang, and Hong-Liang Cui

Doc ID: 283787 Received 29 Dec 2016; Accepted 24 Mar 2017; Posted 24 Mar 2017  View: PDF

Abstract: Interactions of terahertz (THz) radiation with polymer materials have been studied recently with increasing depth and breadth, for purposes of both using polymers in fabricating THz optical components such as lenses, waveplates, and waveguides; and employing THz spectral imaging as a new tool for nondestructive testing of polymer composite structures. Either endeavor cannot even begin without a quantitative knowledge of the complex dielectric permittivity, i.e. the propagation and attenuation properties, of such polymers in the requisite wave band. In this paper, a number of non-polar and non-magnetic polymers, such as polytetrafluoroethylene (PTFE), polypropylene (PP), high-density polyethylene (HDPE), and polymethyl methacrylate (PMMA), are studied for the purpose of determining their complex dielectric permittivity, including its real part and imaginary part, in the wide frequency band from millimeter wave (MMW) to THz wave (75 GHz-1.6 THz), in two ways. The first is a free space method based on a vector network analyzer ( VNA ) covering the frequency region from 75 GHz to 500 GHz, and the second is the THz time-domain spectroscopy (THz-TDS), effective for the region of 100 GHz - 1.6 THz. The results are consistent with available existing data (with discrepancies less than 1% in most cases for both the index of refraction and the absorption coefficient); and where they overlap in frequency coverage, the two methods yield identical results to within measurement error.

A machine learning approach to OAM beam demultiplexing via convolutional neural networks

Timothy Doster and Abbie Watnik

Doc ID: 285198 Received 03 Feb 2017; Accepted 24 Mar 2017; Posted 24 Mar 2017  View: PDF

Abstract: Orbital angular momentum (OAM) beams allow for increased channel capacity in free-space optical communication. These OAM beams are multiplexed together at a transmitter and then propagated through the atmosphere to a receiver where, due to their orthogonality properties, they are demultiplexed. We propose a technique to demultiplex these OAM carrying beams by capturing an image of the unique multiplexing intensity pattern and training a Convolutional Neural Network (CNN) as a classifier. This CNN-based demultiplexing method allows for simplicity of operation as alignment is unnecessary and costly optical hardware is not required. We test our CNN-based technique against a traditional demultiplexing method, conjugate mode sorting, with various OAM mode sets and levels of simulated atmospheric turbulence in a laboratory setting. Furthermore, we examine our CNN-based technique with respect to added sensor noise, number of photon detections, number of pixels, and training set size.

Qualitative and quantitative analysis of mercury in landfill leachates using double-pulse laser-induced breakdown spectroscopy

Carlos Menegatti, Gustavo Nicolodelli, Giorgio Senesi, OTAVIO da SILVA, Hélcio Filho, Paulino Villas-Boas, Bruno Marangoni, and Debora Milori

Doc ID: 286577 Received 10 Feb 2017; Accepted 24 Mar 2017; Posted 24 Mar 2017  View: PDF

Abstract: Laser induced breakdown spectroscopy (LIBS) is showing to be a promising, quick, accurate and practical technique to detect and measure metal contaminants and nutrients in urban wastes and landfill leachates. Although conventional LIBS presents some limitations, such as low sensitivity, when used in the single pulse (SP) configuration if compared to other spectroscopic techniques, the use of the double pulse (DP) configuration represents an adequate alternative. In this work DP LIBS has been applied to the qualitative and quantitative analysis of mercury (Hg) in landfill leachates. The correlation analysis performed between each intensified charge-coupled device (ICCD) pixel and the Hg concentration allowed to choose the most appropriate Hg transition to be used for its measure. The normalization process applied to LIBS spectra to correct physical matrix effects and small fluctuations increased from 0.82 to 0.98 the linear correlation of the calibration curve between LIBS and the reference data. The limit of detection for Hg estimated using DP LIBS was 76 mgKg-1. The cross validation (leave-one-out) analysis yielded an absolute average error of about 20%. These values showed that the calibration models were close to the optimization limit and satisfactory for Hg quantification in landfill leachate

Impact of assisting atmospheric pressure plasma on the formation of micro- and nanoparticles during picosecond-laser ablation of titanium

Stefan Grottker, Wolfgang Viöl, and Christoph Gerhard

Doc ID: 287412 Received 23 Feb 2017; Accepted 23 Mar 2017; Posted 24 Mar 2017  View: PDF

Abstract: In this work, we investigated the generation of particles during pure laser and plasma-assisted laser ablation of titanium. Experiments were performed using a NIR picosecond laser at a wavelength of 1030 nm and a pulse duration of 8 ps. For plasma-assisted ablation, an atmospheric pressure dielectric barrier discharge plasma was applied where the process gas was argon. Quantitative particle distributions at sizes from 10 nm to 10 µm were determined. In addition, we evaluated the amount of ablated material via laser scanning microscopy. The ablated volume was significantly increased by a factor of 2 to 3 in case of plasma-assisted ablation, depending on the applied laser dose. It is shown that the increase in particle volume and number of particles was lower than the ablated volume. However, when applying plasma simultaneously, the generation of small nanoparticles increases notably by a factor of up to 6.63 at a laser dose of 0.7 kJ/mm² for particles with a mean diameter of 10 nm. The results suggest that even smaller particles than measurable are generated. Hence, plasma-assisted laser ablation could enhance the process efficiency, reduce the particle formation and give rise to an increase in generation of nano- or even picoparticles at the same time.

The impact of partial coherence on the apparent optical transfer function derived from the response to amplitude edges

Mojtaba Shakeri, Lucas Van Vliet, and Sjoerd Stallinga

Doc ID: 282355 Received 06 Dec 2016; Accepted 23 Mar 2017; Posted 24 Mar 2017  View: PDF

Abstract: We present an investigation of the impact of partial coherence on optical imaging systems with the focus on Whole Slide Imaging (WSI) systems for digital pathology. The investigation is based on the analysis of the edge response of the optical system, which gives rise to an apparent Optical Transfer Function (OTF) that can be linked to two elementary complex functions Q and U. The function Q is directly related to the Transmission Cross-Coefficient (TCC) and can be identified with the performance function first introduced by Kintner and Stillitto. The function U depends on the TCC in a more involved way. When there are no aberrations the Q-function corresponds to the real part of the apparent OTF and the U function to the imaginary part of the apparent OTF. Close to the incoherent limit the effect of the U function is a mere shift of the edge compared to the fully incoherent case. We propose a new expression for the dependence of the Depth Of Focus (DOF) on spatial frequency and on the partial coherence factor σ, and validate it by simulation. Partial coherence effects are investigated experimentally on a WSI-system with a compact LED-based Köhler illumination unit with variable condenser NA. This unit incorporates a top hat diffuser for providing a reasonably uniform illumination field, with variations below 10% across the imaged Field Of View (FOV). The measurements of the apparent through-focus OTF derived from edges on a custom resolution chart for different σ were substantially in agreement with the simulations. Finding an optimal value for σ is not straightforward as lateral resolution and the level of edge ringing improve with increasing σ, whereas edge contrast and DOF improve with decreasing σ. We assess that the tradeoff for the particular application of WSI systems for digital pathology is optimized for a σ value in the range of 0.55 to 0.75.

Tropospheric haze and colors of the clear twilight sky

Raymond Lee and Duncan Mollner

Doc ID: 285879 Received 31 Jan 2017; Accepted 23 Mar 2017; Posted 24 Mar 2017  View: PDF

Abstract: At the earth’s surface, clear-sky colors during civil twilights depend on the combined spectral effects of molecular scattering, extinction by tropospheric aerosols, and absorption by ozone. Molecular scattering alone cannot produce the most vivid twilight colors near the solar horizon, for which aerosol scattering and absorption are also required. However, less well known are haze aerosols’ effects on twilight sky colors at larger scattering angles, including near the antisolar horizon. To analyze this range of colors, we compare 3D Monte Carlo simulations of skylight spectra with hyperspectral measurements of clear twilight skies over a wide range of aerosol optical depths. Our combined measurements and simulations indicate that: (a) the purest antisolar twilight colors would occur in a purely molecular, multiple-scattering atmosphere, whereas (b) the most vivid solar-sky colors require at least some turbidity. Taken together, these results suggest that multiple scattering plays an important role in determining the redness of the antitwilight arch.

Folded monocentric imager with deformable mirror focus

Glenn Schuster, William Mellette, and Joseph Ford

Doc ID: 286353 Received 13 Feb 2017; Accepted 23 Mar 2017; Posted 24 Mar 2017  View: PDF

Abstract: We describe a catadioptric monocentric imager using an elastic central element focused by deformation of a fold mirror. We show the design of 6 and 12 mm focal length F/2.8 achromats, and compare design performance when focusing by translation of the sensor, translation of the fold mirror, and by spherical mirror deformation. We tested the 12 mm design using a diamond turned polystyrene element as the outer meniscus lens (and mechanical mount), filled with an optical gel in contact with the central aperture and fold mirror, and demonstrate focusing by mechanical deformation of the fold mirror. The resolution at the spherical image surface was inspected by optical relay imaging, yielding a best focus MTF50 of 52.6 lp/mm.

Transparency Measurement of Thin Films with One-Side Optical Access Using Fluorescence Imaging

Amir Farzad Forughi, Boris Stoeber, and Sheldon Green

Doc ID: 283748 Received 27 Dec 2016; Accepted 23 Mar 2017; Posted 23 Mar 2017  View: PDF

Abstract: Optical transparency can be determined by passing light through an object and comparing the intensity of the transmitted light with the intensity of the incident light. This measurement needs optical access to both sides of the object for illumination and measurement. Optical access to both sides of the object may be restricted in some situations due to the presence of an opaque obstacle, lack of physical access, etc. A novel technique of transmittance measurement is presented that is able to determine the transparency of thin film objects with optical access limited to just one side. This method involves mounting the object on a fluorescent substrate, illuminating the object at an excitation wavelength, and observing the light radiated from the object at the fluorescence wavelength. The observed intensity of the light at the fluorescence wavelength is directly related to the transmittance of the object at the excitation and fluorescence wavelengths. This optical configuration eliminates the effect of reflection from the object surface on the quantification of optical transmittance. The technique was used to measure the transmittance of neutral density filters, which were also measured using a conventional transmittance configuration. The difference between the transmittance measured using one-sided optical access and the conventional two-sided configuration was 1% or less. As an example of the utility of the one-sided measurement technique, the transmittance of paper was measured during drying, while the paper sample was sandwiched between a woven dryer fabric and a heater. The relationship between the optical transmittance of paper and its moisture content has been determined previously, and this relationship was used to infer the moisture content of the paper during drying. The moisture content distribution during the drying process is shown to be spatially correlated with the structure of the dryer fabric.

Relationship of the drying process of a corn grain withthe thermal emissivity and optical interference in themid infrared range

Carlos Villaseñor-Mora, Francisco Gantes, Arturo González-Vega, and Victor Hernandez-Gonzalez

Doc ID: 283891 Received 05 Jan 2017; Accepted 22 Mar 2017; Posted 23 Mar 2017  View: PDF

Abstract: A study of the effect of thin layer of free water in corn kernels on the emissivity and interference in the mid infraredrange was performed; the emissivity was measured through thermal infrared images by direct method along theeight days, it allowed to observe that the thick of free water modifies the quantity of emitted energy and theemissivity, however, the measurement of emissivity in the first days or when the layer of free water is not opticallythick the interference caused by the thin film of superficial water averts a correct measurement of the emissivity.This interference effect was studied and characterized finding that the number of oscillations, in the energy of thegrain, observed and counted in a very small area, can be used to compute the thickness of the free water layercontained between the endosperm and the pericarp of the grain.

1.5kW Radially Polarized Beam Irradiated from FAF CO2 Laser Based on Intracavity Triple-axicon Retroreflector and Quarter Wave Phase Retarders

Bo Li, Youyou Hu, Yi Hu, and Jiang Zhao

Doc ID: 285509 Received 23 Jan 2017; Accepted 22 Mar 2017; Posted 23 Mar 2017  View: PDF

Abstract: In this paper, a triple-axicon retroreflector and four quarter wavelength phase retarders are employed in a fast axial flow CO_2 laser system to form a three folds spatial resonator and generate radially polarized beams. The triple-axicon retroreflector serves as azimuthally polarization beams selective element, while the four quarter wavelength phase retarders works as polarization converter. Finally, a stable 1.5kW radially polarized beams is illuminated directly in this laser system.

Widely tunable 2μm continuous and mode-locked fiber laser

Wanzhuo Ma, Tianshu Wang, Yan Zhang, Peng Liu, Yuwei Su, Qingsong Jia, Mingzhe Bi, Peng Zhang, and Huilin Jiang

Doc ID: 285738 Received 26 Jan 2017; Accepted 22 Mar 2017; Posted 22 Mar 2017  View: PDF

Abstract: We propose and experimentally demonstrate a widely tunable mode-locked thulium-doped fiber laser. The laser can operate at both continuous and mode-locked state at different pump power level. A classic nonlinear polarization rotation structure is employed to obtain passive mode-locked laser. A birefringence Lyot filter as a fiber comb filter is used to expand the tuning range. Thanks to the filtering component, the tuning range of continuous laser can reach 127nm (18 -1950nm). The tuning rang of single-wavelength and dual-wavelength mode-locked laser are 94nm (1835-1929nm) and 87nm (1831-1918nm) respectively with the 3.085MHz repetition frequency and 75ps pulse width.

Trajectories variation of optical Bloch oscillations for Airy beam in transversely and longitudinally modulated photonic lattices

Zheng Cao, Xiaojun Li, qinggui tan, Wei Jiang, Dong Liang, and Jinfang Dou

Doc ID: 285460 Received 23 Jan 2017; Accepted 22 Mar 2017; Posted 22 Mar 2017  View: PDF

Abstract: We consider four types of modulated photonic lattices and numerically study the optical Bloch oscillations of Airy beams in these periodic structures. Our results demonstrate that in transversely modulated photonic lattices, the oscillation period enhances and the amplitude reduces as the separation variation index increases. However, the increasing of width variation index could lead to a consistent reduction of oscillation period and amplitude. On the other hand, in three kinds of longitudinally bent photonic lattices, the optical Bloch oscillation trajectories of Airy beams follow the waveguide shape perfectly within the whole propagation length. For another three kinds of refractive index longitudinally varied lattices, the optical Bloch oscillation period and amplitude are limited with the increasing of refractive index, contributing to the presentation of dramatically different Airy propagation trajectories. Our study proposes a new view to manipulate the Airy trajectory in periodic structures.

Thermally stable WLEDs with excellent luminous properties by screen-printing patterned phosphor glass layer on microstructured glass plate

Yang Peng, Xing Guo, Ruixin Li, Hao Cheng, and Mingxiang Chen

Doc ID: 283302 Received 20 Dec 2016; Accepted 22 Mar 2017; Posted 23 Mar 2017  View: PDF

Abstract: In order to improve the luminous properties and thermal reliability of white light-emitting diodes (WLEDs), we proposed a promising phosphor-in-glass (PiG) converter, which was prepared by screen-printing a patterned phosphor glass layer on a microstructured glass plate. The patterned layer achieves 4-quadrant phosphor geometry based on separated yellow Y3Al5O12:Ce3+ (YAG:Ce3+) and red CaAlSiN3:Eu2+ (CASN:Eu2+) phosphor parts. Comparison experiments between the patterned PiG with and without microstructure array (MSA) were conducted at different phosphor glass thicknesses. Consequently, as the phosphor glass thickness of 75 μm, the luminous efficacy (LE) of proposed PiG is increased by 12.5% owing to the reduction of total internal reflection (TIR) at the glass-air interface by the MSA, and the corresponding correlated color temperature (CCT) and color rendering index (CRI) are 3701 K and 85.1, respectively. Furthermore, the CCT deviations of patterned PiG are reduced from 405 to 115 K and 1004 to 548 K by the MSA at the average CCTs of 3800 K and 5500 K, respectively. The results demonstrate that the proposed PiG converter can improve the LE and angular color uniformity (ACU) of multi-components PiG-based WLEDs simultaneously.

3D Cost Aggregation with Multiple Minimum Spanning Trees for Stereo Matching

Lincheng Li, Xin Yu, Shunli Zhang, Xiaolin Zhao, and li zhang

Doc ID: 286217 Received 06 Feb 2017; Accepted 21 Mar 2017; Posted 24 Mar 2017  View: PDF

Abstract: Cost aggregation is one of the key steps in stereo matching problem. In order to improve the aggregation accuracy, we propose a cost aggregation method that can embed MST-based support region filtering into PatchMatch 3D label search rather than aggregating on fixed size patches. However, directly combining PatchMatch label search and MST filtering is not straightforward due to the extremely high complexity. Thus, we develop the multiple MSTs structure for cost aggregation on plenty of 3D labels, and design the tree level random search strategy to find possible 3D labels of each pixel. Extensive experiments show that our method reaches higher accuracy than all other cost aggregation and global optimization methods in different datasets, and currently ranks 1st on Middlebury 3.0 benchmark.

Precise Calibration of Pupil Images in Pyramid Wavefront Sensor

yong liu, Quanquan Mu, Zhaoliang Cao, Lifa Hu, Chengliang Yang, and Li Xuan

Doc ID: 284268 Received 06 Jan 2017; Accepted 21 Mar 2017; Posted 22 Mar 2017  View: PDF

Abstract: The pyramid wavefront sensor (PWFS) is a noval wavefront sensor with several inspiring advantages compared with Shack-Hartmann wavefront sensor. PWFS uses four pupil images to calculate the local tilt of the incoming wavefront. Pupil images are conjugated with telescope pupil so each pixel in pupil image is diffraction-limited by the telescope pupil diameter, thus the sensing error of PWFS is much lower than that of Shack-Hartmann sensor and is related to the extraction and alignment accuracy of pupil images. However, precise extraction of these images is difficult to conduct in practice. Aiming at improving the sensing accuracy, we analyzed the physical model of calibration of PWFS and put forward an extraction algorithm. The process was verified via closed-loop correction experiment. The results showed that the sensing accuracy of PWFS increased after applying the calibration and extraction method.

Nanoscale Schottky contact surface plasmon “point detectors” for optical beam scanning applications

naema Othman and Pierre Berini

Doc ID: 283639 Received 26 Dec 2016; Accepted 21 Mar 2017; Posted 22 Mar 2017  View: PDF

Abstract: We propose and investigate a Schottky contact detector where the contact metal is a nanoscale metal stripe waveguide supporting surface plasmons with strong localisation along the Schottky contact. We consider Au for the metal stripe, p-doped silicon for the semiconductor, operation in the infrared (at 0 = 1550 nm), and internal photoemission as the sub-bandgap detection mechanism. We find that the main surface plasmon mode of operation of the Au stripe exhibits diverging real and imaginary parts of neff with decreasing stripe dimensions, commensurate with increasing confinement. The mode fields are tightly confined to the immediate vicinity of the stripe within a very small area. Coupling efficiencies, responsivities, dark currents and minimum detectable powers are computed. An application envisaged for such nanoscale “point detectors” is optical beam scanning, motivated by the very small area of the photodetector stripe mode relative to, e.g., a Gaussian beam (~500× smaller) such that its field distribution approximates a Dirac delta function in comparison, and by the photocurrent originating primarily from selective absorption of the photodetector stripe mode. The proposed application was verified through numerical simulation, demonstrating that a nanoscale “point detector” can scan a tightly focussed Gaussian beam (2.5 µm diameter at λ0 = 1550 nm) with good resolution and signal-to-noise.

Lensless wide-field single-shot imaging through turbid media based on object-modulated speckles

P Wu, Zi Liang, Xing Zhao, Lei Su, and Lipei Song

Doc ID: 283796 Received 28 Dec 2016; Accepted 21 Mar 2017; Posted 22 Mar 2017  View: PDF

Abstract: The need to image objects through light-scattering materials is common in a range of applications. Different methods have been investigated to acquire the image of the objects when diffusers are presented. In this paper, we demonstrate the object reconstruction with single-shot imaging based on correlography principle and phase retrieval algorithm with coherent illumination. We prove the possibility of reconstructing positive and negative object in both transmission and reflection modes with collimated and scattered light. Formulas for calculating the size of the object from the reconstructed image are presented. We also prove that the object can be retrieved from a small section of the raw speckle image, a property similar to holography. These interesting features will open new doors for imaging applications to wider areas.

Optical pressure and numerical simulation of optical forces

Olav Gaute Helleso

Doc ID: 285674 Received 26 Jan 2017; Accepted 21 Mar 2017; Posted 22 Mar 2017  View: PDF

Abstract: Optical forces on a particle can be calculated using numerical methods and by integrating the Maxwell stress tensor over the surface of the particle. It is shown in this letter that the method gives considerable noise for the radiation force on particles with refractive index close to that of the surrounding medium and that a large number of mesh elements are necessary. It is found preferable to calculate the force from the local optical pressure, as this gives considerably less noise and requires significantly fewer mesh elements. Results are also compared with an analytical model based on Mie theory.

Globally Optimal Camera-and-Rotation-Sensor Calibration with a Branch-and-Bound Algorithm

Yongmoon Park, Youngju Choi, and Yongduek Seo

Doc ID: 275589 Received 31 Jan 2017; Accepted 21 Mar 2017; Posted 24 Mar 2017  View: PDF

Abstract: This paper introduces a globally optimal algorithm to obtain the rotational displacement between the coordinate frames of a rotation sensor and a camera, rigidly attached. Our method minimizes a geometrically meaningful error using a branch-and-bound algorithm to find the global solution. For this, we derive new bounding inequality and corresponding feasibility problem for a top-down efficient search over the rotation space to minimize the L₁, L₂ or L∞-norm error function. Experiments are performed with synthetic and real data sets to show the efficacyof the algorithm.

Method of calculation of internal parameters of liquid lens

Antonin Miks and Jiri Novak

Doc ID: 286106 Received 03 Feb 2017; Accepted 20 Mar 2017; Posted 22 Mar 2017  View: PDF

Abstract: This paper is focused on the problem of determination of internal parameters of fluidic lens composed of two immiscible liquids of different refractive index, which form a tunable refractive interface for changing the focal length of a lens. Formulas are derived for calculation of a radius of curvature of the internal interface between two liquids and refractive indices of liquids using the measurements of the focal length of the lens, positions of focal points and transverse spherical aberration of the lens.

Measuring Spatiotemporal Ultrafast Field Structures of Pulses from Multimode Optical Fibers

Zhe Guang, Michelle Rhodes, and Rick Trebino

Doc ID: 283874 Received 04 Jan 2017; Accepted 20 Mar 2017; Posted 22 Mar 2017  View: PDF

Abstract: Ultrashort pulses emerging from multimode optical fibers are spatiotemporally complex, because inside these fibers the modes have different spatial intensity patterns and experience different propagation velocities and dispersions. To determine the spatiotemporal field from multimode fibers, we applied a technique for the complete measurement of the output pulses called Spatially and Temporally Resolved Intensity and Phase Evaluation Device: Full Information from a Single Hologram (STRIPED FISH). It yields the complete electric field over space and time from multiple digital holograms, simultaneously recorded at different frequencies on a single camera frame. Using femtosecond pulses from a Ti:Sapphire laser, we measured the first few linearly polarized modes (LP01, LP11, LP02, and LP21) inside several few mode fibers. We also generate movies displaying the measured spatial, temporal, and spectral field features.


David Lynch and David Dearborn

Doc ID: 285429 Received 23 Jan 2017; Accepted 20 Mar 2017; Posted 22 Mar 2017  View: PDF

Abstract: Theory and experiments reported here show that overlapping primary and secondary rainbows occur in ice spheres and ice cylinders. So far, no naturally-occur icebows have been reported but they should be relatively easy to observe in icicles.

First airborne in-situ measurement of a glory

Mahen Konwar, Philip Laven, and T. V. Prabha

Doc ID: 285524 Received 23 Jan 2017; Accepted 20 Mar 2017; Posted 22 Mar 2017  View: PDF

Abstract: Whilst making airborne measurements of cloud particles, a bright glory was observed on a thin layer cloud. By deliberately flying through this glory-producing cloud on several occasions, cloud particle size distributions were obtained. We found that warm liquid clouds with narrow cloud droplet size distributions are responsible for producing the observed glory. This paper presents these results and compares the results of Mie theory simulations with an image of the glory.

Probing the germination kinetics of ethanol-treated Bacillus thuringiensis spores

Guiwen Wang, Huajun Chen, Xiaochun Wang, Lixin Peng, Yuan Peng, and Yong-Qing Li

Doc ID: 285520 Received 26 Jan 2017; Accepted 20 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: Bacillus thuringiensis (Bt) is the most widely used microbial insecticide. To clarify the mechanism of bacterialresistance to ethanol toxicity, the present study investigated the effects of 70% (v/v) ethanol at moderatetemperature (65°C) on Bt spore germination by single-cell Raman spectroscopy and differential interferencecontrast microscopy. We found that over 80% of Bt spores were inviable after 30 min of treatment. Moreover,ethanol treatment affected spore germination; the time for initiation of rapid calcium dipicolinate (CaDPA) release(i.e., lag time, Tlag), time taken for rapid CaDPA release (i.e., ΔTrelease), and time required for complete hydrolysis ofthe peptidoglycan cortex of spores (i.e., ΔTlys) were increased with longer treatment times. Alanine-initiatedgermination upon ethanol treatment for 30–90 min showed a 2- to 4-fold longer Tlag, 2- to 3.5-fold longer ΔTrelease,and ~2-fold longer ΔTlys relative to the control. Dodecylamine-initiated germination treated for 15–30 min had 3- to5-fold longer Tlag and 1.4- to 1.7-fold longer ΔTrelease than the control. Germination induced by exogenous CaDPA wasobserved only in a small fraction of spores treated with ethanol for 5 min. Single-cell Raman spectroscopy revealedthat more than 52% of spores lost CaDPA after 30 min of ethanol treatment; these showed reductions in theintensity of 1280 and 1652 cm−1 bands (corresponding to protein α-helical structure) and increases in that of 1245and 1665 cm−1 bands (attributed to irregularities in protein structure). These results indicate that CaDPA in thecore of Bt spores confers resistance to ethanol, and that damage to the spore inner membrane by ethanoltreatment results in CaDPA leakage. Additionally, moderate-temperature ethanol treatment and consequentdenaturation of germination-related proteins affected spore germination, specifically by inhibiting the cortex-lyticenzyme CwlJ. Our findings provide a theoretical basis for the development of more effective methods for killingspore-forming bacteria; microscopy imaging and Raman spectroscopy can provide novel insight into the effects ofchemical agents on microbial cells.

A Numerical Optimization Platform for Precision Glass Molding by Simplex Algorithm

Weidong Liu and Liangchi Zhang

Doc ID: 284741 Received 13 Jan 2017; Accepted 19 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: Precision glass molding (PGM) can fabricate aspherical lens and irregular optical products in a single step; but its applicability is currently limited by the thermally induced residual stresses and lens shape derivation after molding. To remove this barrier, this paper developed a numerical optimization platform for the PGM based on a simplex algorithm and finite element simulation. It was found that the platform can effectively reduce the residual stress in a molded lens through cooling process optimization, and minimise the lens shape derivation by die shape compensation. The platform established can improve the lens quality by PMG and make molded lenses have better quality than those manufactured by ultra-precision machining processes.

Resampling mask method for speckle reduction by amplitudesuperposition in one-shot digital holography

Wenhui Zhang, Liangcai Cao, zhang hua, Hao Zhang, Guofan Jin, and Yunlong Sheng

Doc ID: 281899 Received 05 Dec 2016; Accepted 19 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: One-shot digital holographic imaging has the advantages of high stability and low temporal cost. However, its reconstruction is degraded severely by the laser speckle. Rectangle and ellipse resampling mask method in spatial domain for speckle reduction is proposed. The effectiveness of the method for speckle reduction is explained successfully. In the method, one hologram recorded in a certain size is divided into N=S×T sub-holograms. Then N reconstructed amplitude images are calculated from the corresponding sub-holograms. Benefitting from speckle’s random distribution, superimposing these N uncorrelated amplitude images would lead to a final reconstructed image with reduced speckle. Normalized relative standard deviation values of the reconstructed image are in good agreement with the asymptotical law. The maximum relative errors between experiment results and theoretical values are below 7.2%. Effect of the method on the spatial resolution of the reconstructed image is also quantitatively evaluated. Experimental and simulation results prove the feasibility and effectiveness of the proposed method.

Phosphor-based light conversion for miniaturized tools for optogenetic research

Deepak Dinakaran, Christian Goßler, Christian Mounir, Oliver Paul, Ulrich Schwarz, and Patrick Ruther

Doc ID: 276467 Received 23 Sep 2016; Accepted 19 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: This paper describes the application of phosphor-based light conversion for its use in optogenetic experiments to tailor the wavelength of light emitted from implantable miniaturized light sources. Gallium-nitride-based blue light-emitting diodes are used in combination with orthosilicate phosphor immersed in an epoxy matrix and emitting in the yellow wavelength range. The miniaturization of the phosphor-containing polymer droplets towards diameters as small as 300 µm provides the compatibility with implantable optical probes. The parameter study applied here varied the concentration of the phosphor material in the polymer matrix as well as the droplet height in order to tailor the characteristics of blue-to-yellow light conversion.

Operation of Ho:YAG ultrafast laser inscribed waveguide lasers

Sean McDaniel, Fiona Thorburn, Adam Lancaster, Ronald Stites, Gary Cook, and Ajoy Kumar Kar

Doc ID: 279302 Received 09 Dec 2016; Accepted 19 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: We report fabrication and operation of multi-Watt level waveguide lasers utilizing holmium doped yttrium aluminum garnet (Ho:YAG). The waveguides were fabricated using Ultrafast Laser Inscription (ULI), which relies on a chirped pulse ytterbium fiber laser to create depressed cladding structures inside of a material. A variety of waveguides were created inside of the Ho:YAG sample. We demonstrate output powers of ~2W from both a single mode 50 μm waveguide and a multimode 80 μm waveguide. This effort marks the first demonstration of ULI waveguide lasers in Ho:YAG. In addition, laser action from a co-doped Yb:Ho:YAG sample under in-band pumping conditions was demonstrated.

The Dimensional Properties of Laguerre-Gaussian Vortex Beams

Jie Zhang, Sujuan Huang, Fuquan Zhu, Wei Shao, and Musheng Chen

Doc ID: 282405 Received 08 Dec 2016; Accepted 19 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: We propose the dimensional properties of Laguerre-Gaussian vortex beams theoretically and numerically. The analytical expressions of inner and outer radii are given out and proved to be proportional to the transverse beam size, when the topological charge remains. The ratio of the outer radius and inner radius only depends on the topological charge, having nothing to do with the waist radius and the propagation distance. And the ratio decreases as the topological charge increases. Based on spatial light modulator loaded with computer generated holograms, we generate LG vortex beams. The experimental results agree excellently with numerical simulations. The research may provide useful insight in the study of the optical vortex beam and its further applications.

Interaction between bubble and metal target for underwater laser propulsion

Hao Qiang, Jun Chen, Bing Han, Yunxiang Pan, Hongchao Zhang, Shen Zhong-Hua, Jian Lu, and Xiaowu Ni

Doc ID: 286328 Received 07 Feb 2017; Accepted 19 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: Optical beam deflection method and high-speed photograph method were employed to investigate the interaction mechanism between the laser-induced bubble and the metal target for underwater laser propulsion. A preliminary theory was proposed to reveal the step increases of the kinetic energy transferred to the target during the process of increasing the incident laser energy. This theory also helped to explain the increasing coupling efficiency with incident laser energy for underwater laser propulsion.

Optimization of excitation of fibre Fabry-Perot tunable filters used in swept sources using phase correction method

Mohammad Avanaki and Adrian Podoleano

Doc ID: 284179 Received 16 Mar 2017; Accepted 19 Mar 2017; Posted 23 Mar 2017  View: PDF

Abstract: In this paper, we investigate a phase correction method for compensation of the nonlinearity of conventional wavelength swept laser sources based on a fiber Fabry-Perot tunable filter as a wavelength selective element. A triangular signal is commonly used to drive the filter. We however extracted zero crossings from the interferogram and modified the shape of the triangular signal accordingly. This algorithm was tested for different values of optical path length differences (OPDs). A significant compensation for the non-linearity of the filter was observed.

Tolerancing the alignment of large-core optical fibers, fiber bundles and light guides using a Fourier approach

Travis Sawyer, Ryan Petersberg, and Sarah Bohndiek

Doc ID: 282693 Received 22 Dec 2016; Accepted 18 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: Optical fiber technology is found in a wide variety of applications to flexibly relay light between two points, enabling information transfer across long distances and allowing access to hard-to-reach areas. Large-core optical fibers and light guides find frequent use in illumination and spectroscopic applications; for example, endoscopy and high-resolution astronomical spectroscopy. Proper alignment is critical for maximizing throughput in optical fiber coupling systems; however, there currently are no formal approaches to tolerancing the alignment of a light guide coupling system. Here, we propose a Fourier Alignment Sensitivity (FAS) algorithm to determine the optimal tolerances on the alignment of a light guide by computing the alignment sensitivity. The algorithm shows excellent agreement with both simulated and experimentally measured values and improves on the computation time of equivalent ray tracing simulations by two orders of magnitude. We then apply FAS to tolerance and fabricate a coupling system, which is shown to meet specifications, thus validating FAS as a tolerancing technique. These results indicate that FAS is a flexible and rapid means to quantify the alignment sensitivity of a light guide, widely informing the design and tolerancing of coupling systems.

Linear frequency modulated continuous wave ladar system for synthetic aperture imaging

Guangzuo Li, wang ran, Ziqi Song, Keshu Zhang, Yirong Wu, and Jie Pan

Doc ID: 282195 Received 07 Dec 2016; Accepted 18 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: A novel and high-efficiency linear frequency modulated continuous wave (FMCW) ladar system for synthetic aperture (SA) imaging is proposed and experimentally demonstrated. This novel system generates wide-bandwidth linear FMCW ladar signal by employing an electro-optic LiNbO3-I&Q modulator with an effective bias controller. The effectiveness of the proposed system is experimentally validated. Optical synthetic aperture images are obtained by using two 0.41-cm aperture diameter telescopes at the distance of 1 km and the resolution is about 4 cm. A resolution improvement by about 10 times is achieved when compared to the conventional real aperture imaging system.

An All Fiber-Optic Acoustic Sensor Array for Real-Time Sound Source Localization

Jian Wang, Hongyan Wu, and Bo Jia

Doc ID: 283789 Received 28 Dec 2016; Accepted 18 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: Real-time sound source localization has been widely realized by the conventional microphone array for the present. And fiber-optic microphones have many advantages over conventional microphones. In the present work, an all fiber-optic acoustic array system with a wavelength-division multiplexing (WDM) scheme is proposed, which has a high sensitivity and significant superiority in high-frequency signal detection, and can be applied in harsh environments. The system also has advantages of simple construction and low cost. Real-time sound source localization is realized through the system.

Iterative reconstruction of scene depth with fidelitybased on light field data

Chang Liu, Jun Qiu, and Songnian Zhao

Doc ID: 283972 Received 10 Jan 2017; Accepted 17 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: Depth reconstruction from the light field, as a new depth extracting approach, is a vibrant research field in the computational imaging. In this paper, depth reconstruction from the light field was taken as an optimization problem by analyzing the forward and inverse models. The forward and inverse models present the connection between the light field and the depth of the scene. We proposed an iterative method for scene depth reconstruction with fidelity from 4D light field data. The objective functional of the optimization problem entails three terms, in which the matching term is formed as the fidelity term, while the gradient term and classification term are constituted as the penalty terms. The iterative ethod minimized the objective functional via correcting mismatching pixels iteratively. In this way, the reconstruction accuracy of the scene depth was significantly improved with high robustness, especially in the weak texture and occlusion regions. The experimental results show that the depth map with high accuracy can be reconstructed by the iterative method, in align with high depth resolution in the weak texture and occlusion regions. The accurate 3D surface in the field of view can be achieved using the depth information reconstructed from the 4D light field.

Development of an X-ray eight-image Kirkpatrick–Baez diagnostic system for China’s laser fusion facility

Yaran Li, Baozhong Mu, QING XIE, Yanan He, Zhiqiang Chen, Zhanshan Wang, Zhurong Cao, Jianjun Dong, Shenye Liu, and Yongkun Ding

Doc ID: 280170 Received 08 Nov 2016; Accepted 17 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: This article presents the development of an X-ray eight-image Kirkpatrick–Baez (KB) diagnostic system to be usedat China’s Shenguang-Ⅲ (SG-Ⅲ) laser facility in aspects of the optical design, multilayers, and online/offline tests.Six pieces of concave spherical substrates are used for constituting a special optical structure. Dual-periodic W/Cmultilayers are used for high reflectivity and large angular bandwidth of ~0.1°. The global spatial resolution is ~5μm in ±100 μm range. The schemes of system installation, transport, collimation, and image acquisition at China’sSG-Ⅲ facility are also discussed.

Common-path digital holographic microscopy for near-field phase imaging based on surface plasmon resonance

Jianlin Zhao, Siqing Dai, Chaojie Ma, Jianglei Di, and Jiwei Zhang

Doc ID: 285284 Received 19 Jan 2017; Accepted 16 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: We develop a common-path digital holographic microscopy based on prism-coupling surface plasmon resonance (SPR) for near-field phase imaging. A single beam splitter with specific configuration is introduced in SPR imaging system to realize off-axis holographic recording. By measuring the phase shift of the reflected light at SPR with high temporal stability exploiting the proposed holographic microscopy, near-field characteristic measurement can be realized. With its simplicity, vibration isolation and inherent capability of phase curvature compensation, the recommended system shows advanced performances of monitoring tiny index variations and imaging biological tissues.

Gaussian beam transformed by the double-phase-ramp converter.

Ann Khoroshun, Aleksandr Bekshaev, Julia Kirichenko, Oleksandr Ryazantsev, and Aleksey Chernykh

Doc ID: 285814 Received 30 Jan 2017; Accepted 16 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: We analyze transformations of circular Laguerre-Gaussian beams with zero radial index after passage through the double-phase-ramp (DPR) converter and study the behavior of optical vortices in the propagating transformed beam. Direct and inverse DPR converters are considered, and informative features of the complete set of optical vortices are revealed. For the input beam with even azimuthal index, such a reaction may cause the sign reversal of the axial OV. The results can be used for creation of light beams with prescribed singular skeleton, for the beam diagnostics and in high-resolution metrology.

Infrared spectroscopy of secondary organic aerosol precursors and investigation of the hygroscopicity of SOA formed from the OH reaction with guaiacol and syringol

Waed Ahmad, Cecile Coeur, Alexandre Tomas, Thomas Fagniez, Jean-Blaise Brubach, and Arnaud Cuisset

Doc ID: 280887 Received 24 Nov 2016; Accepted 16 Mar 2017; Posted 16 Mar 2017  View: PDF

Abstract: ATR-FTIR synchrotron analyses supplemented by DFT anharmonic calculations have been undertaken to study fundamental vibrational signatures of guaiacol and syringol, two methoxyphenol compounds found at the highest concentrations in fresh wood smoke and precursors of secondary organic aerosols (SOA) affecting radiative balance and chemistry of the atmosphere. Nitroderivatives of these two compounds have been also studied experimentally for nitroguaiacol and theoretically for nitrosyringol. All the active fundamental vibrational bands have been assigned and compared to available gas phase measurements providing a vibrational database for the analysis of SOA produced by atmospheric oxidation of methoxyphenols. In addition, the SOA formed in an atmospheric simulation chamber from the OH reaction with guaiacol and syringol were analysed using the ATR-FTIR synchrotron spectroscopy and their hygroscopic properties were also investigated. The vibrational study confirms that nitroguaiacol and nitrosyringol are the main oxidation products of methoxyphenols by OH and are key intermediate in the SOA production. The hydration experiments highlight the hydrophilic and hydrophobic characters of nitrosyringol and nitroguaiacol, respectively.

Graphene-based near-field optical microscopy: High-resolution imaging using reconfigurable gratings

Sandeep Inampudi, Jierong Cheng, and Hossein Mosallaei

Doc ID: 282621 Received 16 Dec 2016; Accepted 15 Mar 2017; Posted 16 Mar 2017  View: PDF

Abstract: High resolution and fast-paced optical microscopy is a requirement for current trends in biotechnology and material industry. The most reliable and adapted technique so far to obtain higher resolution than conventional microscopy is near-field scanning optical microscopy (NSOM) that suffers from its slow paced nature. Stemming from the principles of diffraction imaging, we present a fast-paced graphene-based scanning-free wide-field optical microscopy that provides image resolutions competing with NSOM. Instead of spatial scanning of a sharp tip, we utilize active reconfigurable nature of graphene’s surface conductivity to vary the diffraction properties of a planar digitized atomically thin graphene sheet placed in the near-field of an object. Scattered light through various realizations of gratings is collected at the far-field distance and post-processed using transmission function of surface gratings developed on the principles of rigorous coupled wave analysis. We demonstrate image resolutions of the order of λ_0/16 using computational measurements through binary graphene gratings and numerical post-processing. We also present an optimization scheme based on genetic algorithm to pre-design the unit cell structure of the gratings to minimize the complexity of post-processing methods. We present and compare the imaging performance and noise tolerance of both grating types.

Measurement of the linear thermo-optical coefficient of Ga₀.₅₁In₀.₄₉P using photonic crystal nanocavities

Sergei Sokolov, Jin Lian, Sylvain Combrié, Alfredo De Rossi, and Allard Mosk

Doc ID: 283078 Received 19 Dec 2016; Accepted 15 Mar 2017; Posted 15 Mar 2017  View: PDF

Abstract: Ga₀.₅₁In₀.₄₉P is a promising candidate for thermally tunable nanophotonic devices due to its low thermal conductivity. In this work we study its thermo-optical response. We obtain the linear thermo-optical coefficient dn/dT by investigating the transmission properties of a single mode-gap photonic crystal nanocavity.

Amplitude versus phase effects in extreme ultraviolet lithography mask scattering and imaging

Patrick Naulleau, Markus Benk, Kenneth Goldberg, Eric Gullikson, Anoine Wojdyla, Yow-Gwo Wang, and Andrew Neureuther

Doc ID: 283458 Received 23 Dec 2016; Accepted 15 Mar 2017; Posted 15 Mar 2017  View: PDF

Abstract: It is now well established that extreme ultraviolet (EUV) mask multilayer roughness leads to wafer-plane line-width roughness (LWR) in the lithography process. Analysis and modeling done to date has assumed, however, that the roughness leading to scatter is primarily a phase effect and that the amplitude can be ignored. Under this assumption, simple scattering measurements can be used to characterize the statistical properties of the mask roughness. Here we explore the implications of this simplifying assumption by modeling the imaging impacts of the roughness amplitude component as a function of the balance between amplitude and phase induced scatter.In addition to model-based analysis, we also use an EUV microscope to compare experimental through focus data to modeling in order to assess the actual amount of amplitude roughness on a typical EUV multilayer mask. The results indicate that amplitude roughness accounts for less than 1% of the total scatter for typical EUV masks.

A new efficient acoustooptic crystal, TlInS2: Acoustic and elastic anisotropy

Iryna Martynyuk-Lototska, Ihor trach, Oleksandr KOKHAN, and Rostyslav Vlokh

Doc ID: 285974 Received 01 Feb 2017; Accepted 15 Mar 2017; Posted 16 Mar 2017  View: PDF

Abstract: We have studied experimentally the acoustic wave velocities for TlInS2 crystals and determined all components of their elastic stiffness and compliance tensors. It has been found that TlInS2 reveals small elastic anisotropy with respect to normal mechanical stresses. The compliance components S44 and S55 are very large, thus suggesting that the TlInS2 crystals are extremely compliant to the shear stresses in the cleavage plane. We have also revealed that the velocities of some of the quasi-transverse waves are very low (~ 725 m/s), leading to extremely high acoustooptic figures of merit (~ 2200–9000 10–15 s3/kg). This implies that the crystals under study can prove to be a very efficient acoustooptic material.

A wide-band spectrum analysis of ultra-high frequency radio-wave signals due to an advanced one-phonon non-collinear anomalous light scattering

Alexandre Shcherbakov and Adan Omar Arellanes Bernabe

Doc ID: 286731 Received 15 Feb 2017; Accepted 15 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: We present principally new acousto-optical cell providing an advanced wide-band spectrum analysis of ultra-high frequency radio-wave signals. For the first time we apply recently developed approach with the tilt angle to a one-phonon non-collinear anomalous light scattering. In contrast to earlier cases, now one can exploit regime with the fixed optical wavelength for processing a great number of acoustic frequencies simultaneously in the linear regime. The chosen for cell rutile-crystal combines a moderate acoustic velocity with low acoustic attenuation and allows us a wide-band data processing within GHz-frequency acoustic waves. We have created and experimentally tested a 6 cm aperture rutile-made acousto-optical cell providing the central frequency 2.0 GHz, frequency bandwidth ~ 0.52 GHz with the frequency resolution about 68.3 KHz and ~ 7620 resolvable spots. Similar cell permits designing an advanced ultra-high-frequency arm within recently developed multi-band radio-wave acousto-optical spectrometer for astrophysical studies. This spectrometer is intended to operate with a few parallel optical arms for processing the multi-frequency data flows within astrophysical observations. Keeping all the instrument’s advantages of previous schematic arrangement, now one can create the highest-frequency arm using the developed rutile-based acousto-optical cell. It permits optimizing the performances inherent in that arm via regulation of both the central frequency and the frequency bandwidth for spectrum analysis.

Study of a reflection grating used in Littrow mount

David Capps

Doc ID: 286727 Received 15 Feb 2017; Accepted 14 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: The near and far fields of a finite conductivity metallic grating with symmetrical triangular facets, used in Littrow mount, are studied. A new Green’s function approach, based on the Hertz vector, is introduced, and used to propagate throughout a two dimensional domain. The field quantity of primary interest is Poynting’s vector; however, the stored power is also calculated. In assessing the fields generated by the propagator, a quasiperiodic dependence of output characteristics on the grating depth to period ratio, discussed in the literature, is also found in the present study. With a plane wave incident on the grating, geometrical relationships between the incident wavevector and the grating surfaces have interesting consequences

Real-time Polarization Imaging Algorithm for Camera-based Polarization Navigation Sensors

Hao Lu, kaichun zhao, Zheng You, and Kaoli Huang

Doc ID: 282704 Received 12 Dec 2016; Accepted 14 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: Biologically inspired polarization navigation is a promising approach due to its autonomous nature, high precision, and robustness. Many researchers have built point source-based and camera-based polarization navigation prototypes in recent years. Camera-based prototypes can benefit from their high spatial resolution but incur a heavy computation load. The pattern recognition algorithm in most polarization imaging algorithms involves several non-linear calculations that impose significant computation burden. In this paper, the polarization imaging and pattern recognition algorithms are optimized through reduction to several linear calculations by exploiting the orthogonality of the Stokes parameters without affecting precision according to the features of the solar meridian and the patterns of the polarized skylight. The algorithm contains a pattern recognition algorithm with a Hough transform as well as orientation measurement algorithms. The algorithm was loaded and run on a digital signal processing (DSP) system to test its computational complexity. The test showed that the running time decreased to several tens of milliseconds from several thousand milliseconds. Through simulations and experiments, it was found that the algorithm can measure orientation without reducing precision. It can hence satisfy the practical demands of low computational load and high precision for use in embedded systems.

Design and Simulation of Reflectarray Metasurfaces in the Visible Regime

Salma Alrasheed and Enzo Di Fabrizio

Doc ID: 282994 Received 16 Dec 2016; Accepted 14 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: Metasurfaces are new promising ultrathin materials that can enable many novel optical devices due to its ability to act as a discontinuity interface that introduces an abrupt change in amplitude, phase and sometimes the polarization of the incident light at the wavelength scale. Therefore they can function as flat optical elements. Here, we investigate the anomalous reflection of light for TM polarization for normal and oblique incidence in the visible regime. We propose gradient phase gap surface plasmon (GSP) metasurfaces that exhibit high conversion efficiency (up to 96.6% of total reflected light) to the anomalous reflection angle for blue, green and red wavelengths at normal and oblique incidence, and where light polarization is unchanged after the reflection.

Frequency comb calibrated frequency-sweeping interferometry for absolute group refractive index measurement of air

Yang Lijun, Xuejian Wu, Haoyun Wei, and Yan Li

Doc ID: 285034 Received 17 Jan 2017; Accepted 14 Mar 2017; Posted 15 Mar 2017  View: PDF

Abstract: The absolute group refractive index of air at 1545 nm is measured in real time using frequency-sweeping interferometry calibrated by an optical frequency comb. The group refractive index of air is calculated from the calibration peaks of the laser frequency variation and the interference signal of the two beams passing through the inner and outer regions of a vacuum cell when the frequency of a tunable external cavity diode laser is scanned. We continuously measure the refractive index of air for 2 h, which shows that the difference between measured results and Ciddor equation is less than 9.3×10¯⁸ and the standard deviation of that difference is 5.8×10¯⁸. The relative uncertainty of the measured refractive index of air is estimated to be 8.6×10¯⁸. The data update rate is 0.2 Hz, making it applicable under conditions where air refractive index fluctuates fast.

Research on intelligent algorithms for amplitude optimization of wavefront shaping

Qi Feng, Bin Zhang, liu zhipeng, Chengyou Lin, and Ding Yingchun

Doc ID: 285043 Received 17 Jan 2017; Accepted 14 Mar 2017; Posted 15 Mar 2017  View: PDF

Abstract: This paper demonstrates further research on intelligent algorithms of binary amplitude optimization for wavefront shaping by numerical simulations. A better fitness function of genetic algorithm (GA) has been presented after a comparative analysis of enhancement. With this new discriminant, we have achieved a relative enhancement of 0.225, which is higher than the theoretical value (0.159). In addition, we have also proposed a kind of modified particle swarm optimization algorithm (PSO), which has a higher enhancement than the unmodifed PSO and a faster convergence speed than the GA. These studies provide remarkable insights into future exploration of intelligent algorithms for wavefront shaping.

Polarization based spatial filtering for directional andnon-directional edge enhancement using S-waveplate

B.S.Bhargava Ram, Paramasivam Senthilkumaran, and Anurag Sharma

Doc ID: 286143 Received 03 Feb 2017; Accepted 14 Mar 2017; Posted 15 Mar 2017  View: PDF

Abstract: Using polarization as an additional parameter apart from amplitude and phase in spatial filtering experimentsoffer additional advantages and possibilities. An S- waveplate that can convert a linearly polarizedlight into radially or azimuthally polarized light, can also be used for isotropic edge enhancement. Foranisotropic edge enhancement introduction of a polarizer at the output was recommended and edge selectionwas done by orientation of the polarizer. But the full potential of the S-waveplate as a spatial filterhas not been exploited so far. Unlike the standard amplitude and phase based Fourier filters, which areindependent to the state of polarization of the illuminating beam, the S-waveplate acts in a different waydepending on state of polarization. The edge selection need not be carried out by changing the orientationof the polarizer. With a fixed polarizer at the output, we show that either isotropic or anisotropicedge enhancement in any desired orientation can be performed by operating the same spatial filter setupin different illuminating polarization states.

Tunable femtosecond near-IR source by pumping an OPA directly with a 90 MHz Yb:fiber source

Markus Betz, Jan Mundry, and Jan Lohrenz

Doc ID: 286194 Received 06 Feb 2017; Accepted 14 Mar 2017; Posted 15 Mar 2017  View: PDF

Abstract: Up to 400 mW of near-IR (1370 nm – 1500 nm) femtosecond pulses are generated from an optical parametric amplifier directly driven by a Yb:fiber oscillator delivering 100 fs pulses at 1036 nm. The process is seeded by a stable supercontinuum obtained from a photonic crystal fiber. We use a single pass through a 3 mm, magnesium oxide-doped, periodically poled LiNbO3 down-conversion crystal to produce a near-IR pulse train with a remarkable power stability of 1.4% (RMS) during one hour. Tuning is achieved by the temperature and the poling period of the nonlinear crystal.

Multi-Point Temperature Sensing Using Linear-Cavity Lasing System

Hiroki Kishikawa, Mao Okada, Kazuto Takahashi, Po-Jung Chen, Nobuo Goto, Yi-Lin Yu, and Shien-Kuei Liaw

Doc ID: 283286 Received 20 Dec 2016; Accepted 14 Mar 2017; Posted 16 Mar 2017  View: PDF

Abstract: A multi-point fiber sensing system consisting of linear cavity laser was proposed. First, optical nonlinearity in amplification with a semiconductor optical amplifier (SOA) was discussed to clarify the effects of gain saturation and four-wave mixing (FWM) on the proposed multi-channel sensing system. Then, lasing conditions in the linear cavity laser consisting of an SOA, an arrayed waveguide grating (AWG), and fiber Bragg gratings (FBGs) were theoretically investigated. The multi-wavelength lasing power was found to be limited mainly by gain saturation in the SOA. Next, multi-wavelength lasing in the cavity consisting of an SOA, an AWG, a loop mirror, and fiber mirror reflectors was experimentally demonstrated up to eight channels. Finally, two-channel temperature sensing using two FBGs as the sensing elements was experimentally confirmed.

Electromagnetic optimization of the IMJP tool and its application in millimeter-scale discontinuous structure processing

Haobo cheng, Hao Yang, Hengyu Wu, and Tan Wang

Doc ID: 283116 Received 19 Dec 2016; Accepted 14 Mar 2017; Posted 14 Mar 2017  View: PDF

Abstract: To meet the special demands in small scale discontinuous optical surface fabrication, the integrated magnetorheological jet polishing (IMJP) tool with multiple motion degrees is introduced in this paper. Four jetting models are implemented and investigated by means of the IMJP tool for practical manufacture. To ensure steady jetting in a long distance, ideal distribution characteristics of the magnetic field in the structure is proposed, based on electromagnetic theory. The magnetic field distribution is simulated subsequently using finite element analysis (FEA) method and three key parameters in the IMJP tool structure are optimized through the simulations. The actual magnetic flux density is measured and spot polishing experiments are conducted in different stand-off distance, verifying the effectiveness of the optimization. Processing experiment of a millimeter scale structure with milling tool marks located on a surface with non-uniform curvatures was conducted utilizing the IMJP tool. The roughness of the polishing region converged to 4.86 nm Ra from a low initial quality after processing, and the tool marks have been efficiently removed. The experimental results reveal the reliability of the setup design and the remarkable smoothing ability of the IMJP tool for small complex structures.

Observation of dehydration dynamics in biological tissues with terahertz digital holography

Han Guo, Xinke Wang, Yan Zhang, Peng Han, Wenfeng Sun, Shengfei Feng, and Jiasheng Ye

Doc ID: 281735 Received 29 Nov 2016; Accepted 14 Mar 2017; Posted 15 Mar 2017  View: PDF

Abstract: A terahertz (THz) digital holographic imaging system is utilized to investigate natural dehydration processes in three types of biological tissues, including cattle, mutton, and pork. An image reconstruction algorithm is applied to remove the diffraction influence of THz waves and further improve clarity of THz images. From THz images of different biological specimens, distinctive water content as well as dehydration features of adipose and muscle tissues are precisely distinguished. By analyzing THz absorption spectra of these samples, temporal evolution characteristics of the absorbances for adipose and muscle tissues are described and compared in detail. Discrepancies between water retention ability of different animal tissues are also discussed. The imaging technique provides a valuable measurement platform for biological sensing.

Experimental study of propagation properties of vortex beam in oceanic turbulence

Zhenglin Liu, Jialin Chen, and Daomu Zhao

Doc ID: 285452 Received 23 Jan 2017; Accepted 13 Mar 2017; Posted 13 Mar 2017  View: PDF

Abstract: The spectral density of vortex beams always change on propagation through oceanic turbulence, which is influenced by parameters of turbulence. This property is usually researched only by numerical simulation. Recently, a new method by spatial light modulator (SLM) can be used to show various turbulence in laboratory, which makes it possible to construct a system of a beam passing through turbulence by experiment. We investigate a vortex beam propagating through oceanic turbulence with spiral phase plate and SLM in laboratory and obtain the spectral density images by charge-coupled device. Compared with simulation results, the applicability of this method is more valid.

Experimental analysis of stress fields of rotating structural elements by means of reflection photoelasticity

Peter Frankovský, Oskar Ostertag, Eva Ostertagová, František Trebuňa, Ján Kostka, and Marek Výrostek

Doc ID: 284075 Received 25 Jan 2017; Accepted 13 Mar 2017; Posted 13 Mar 2017  View: PDF

Abstract: Subject of this paper is an experimental stress analysis of a rotor with symmetrical arm end and a rotor with asymmetrical arm end. Stress state of the analyzed rotors is caused by centrifugal forces. The experiment was carried out by means of reflection photoelasticity and the experimental solution was focused on periodical dynamic effects which required the use of stroboscopic white light. The resulting principal normal stresses were compared with stress values which were obtained by analytical calculation and by numerical means of the finite element method.

Signal restoration method for restraining range walk error of Gm-APD lidar in acquiring merged 3D image

Lu Xu, Yu Zhang, Zhang Yong, Long Wu, Chenghua Yang, Xu Yang, Zijing Zhang, and Yuan Zhao

Doc ID: 284324 Received 09 Jan 2017; Accepted 13 Mar 2017; Posted 13 Mar 2017  View: PDF

Abstract: The fluctuation of signal photoelectrons number will cause a range walk error, which deeply depends on the target intensity. For a nanosecond-pulsed laser, the range walk error of the traditional time-of-flight is deteriorative. A new signal restoration method, based on Poisson probability response model and center-of-mass algorithm, is proposed to restrain the range walk error. We obtain a high-precision depth and intensity merged 3D image. The range accuracy is 0.6 cm and intensity error is less than 3%.

Microsensors Based on Whispering-Gallery-Mode in AlGaN Microdisks Undercut by Hydrogen-Environment Thermal Etching

Tetsuya Kouno, Masaru Sakai, Takeshima Hoshi, Suzuki Sho, Akihiko Kikuchi, Katsumi Kishino, and Kazuhiko Hara

Doc ID: 284489 Received 10 Jan 2017; Accepted 13 Mar 2017; Posted 13 Mar 2017  View: PDF

Abstract: AlGaN microdisks were fabricated via a top-down process using electron-beam lithography, inductively coupled plasma reactive-ion etching, and hydrogen-environment thermal etching from commercial epitaxial wafers with a 100~300 nm thick AlGaN layer grown on c-plane GaN layer by metal-organic chemical vapor deposition. The hydrogen-environment thermal etching performed well in undercutting the AlGaN microdisks owing to the selectively etching for the GaN layer. The AlGaN microdisks acted as the Whispering-gallery-mode (WGM) optical microresonators, exhibiting sharp resonant peaks in room temperature photoluminescence spectra. The evanescent component of the WGM is influenced by the ambient condition of the microdisk, resulting in the shift of the resonant peaks. The phenomenon is considered to be used to microsensors. Using the WGM in the AlGaN microdisks, we demonstrated microsensors and microsensor system, which can potentially be used to evaluate bio and chemical actions in a microscale area in real time.

Superlensing Microscope Objective Lens

Bing Yan, Zengbo Wang, Alan parker, Yu-kun Lai, John Thomas, Liyang Yue, and James Monks

Doc ID: 281397 Received 23 Nov 2016; Accepted 13 Mar 2017; Posted 13 Mar 2017  View: PDF

Abstract: Conventional microscope objective lenses are diffraction limited; they cannot resolve subdiffraction features of size smaller than 250-300 nm under white lighting condition. New innovations are required to overcome such limit. In this paper, we propose and demonstrate a new superlensing objective lens which possesses a resolution of 100 nm, offering two times resolution improvement over conventional objectives. This is accomplished by integrating a conventional microscope objective lens with a superlensing microsphere lens using a customized lens adaptor. The new objective lens was successfully demonstrated for label-free super-resolution imaging of 100 nm-sized engineering and biological samples, including a Blu-ray disc sample, semiconductor chip and adenoviruses. Our work opens a new door to develop a generic optical superlens, which may transform the field of optical microscopy and imaging.

Energetic materials identification by laser-induced breakdown spectroscopy combined with artificial neural network

Amir Hossein Farhadian, Masoud Kavosh Tehrani, Mohammad Keshavarz, and seyyed mohammad reza darbani

Doc ID: 282127 Received 02 Dec 2016; Accepted 13 Mar 2017; Posted 13 Mar 2017  View: PDF

Abstract: In this study, for first time, a combination of laser-induced breakdown spectroscopy (LIBS) technique and artificial neural network (ANN) analysis has been implemented for the identification of energetic materials, including TNT, RDX, black powder and propellant. Also, Aluminum, Copper, Inconel and graphite have been used for more accurate investigation and comparison. After LIBS test and spectrum acquisition on all samples in both air and Argon ambient, optimized neural networks (NN) was designed by LIBS data. Based on input data, three ANN algorithms are proposed: first is fed with the whole LIBS spectra in air (ANN1) and second with the principle component analysis (PCA) scores of each spectrum in air (ANN2) and the other with the PCA scores of spectrum in Ar (ANN3). According to results, error of network is very low in ANN2 and 3 and the best identification and discrimination was obtained by ANN3. After these in order to validation and more investigation of this combined method we also used Al/RDX standard samples for analysis.

Random phase-shifting algorithm by constructing orthogonal phase shifting fringe patterns

Hubing Du, Jingjing Yan, and Jianhua Wang

Doc ID: 285420 Received 26 Jan 2017; Accepted 12 Mar 2017; Posted 13 Mar 2017  View: PDF

Abstract: The intensity distribution of fringe patterns become nonsinusoidal in the real testing environments. Thus the performance of existing phase shift extraction algorithms may be affected, which usually compute the desired phase shift by arccosine function or arcsine function. In the presented paper, we report an arctangent function based technique to solve this disturbance. First, two orthogonal fringe patterns are constructed through subtraction and addition of two background removed images. Second, the unequal amplitude between two new fringe patterns is eliminated using normalization process. Third, the phase shift is determined by computing the norms of two new images. The proposed method is fast and can be implemented easily in many applications. We verify the algorithm performance and robustness using both simulated and experimental data, indicating high accuracy of the presented method.

Stable nanosecond passively Q-switched all-fiber Erbium-doped laser with a 45° tilted fiber grating

Tianxing Wang, zhijun yan, Chengbo Mou, Kaiming Zhou, and Lin Zhang

Doc ID: 284365 Received 09 Jan 2017; Accepted 12 Mar 2017; Posted 13 Mar 2017  View: PDF

Abstract: Nanosecond passive Q-switching generation from an all-fiber Erbium-doped laser with a UV inscribed 45° tilted fiber grating (TFG) is systematically demonstrated. The 45° TFG is employed as a polarizer together with two polarization controllers (PCs) to realize the nonlinear polarization rotation (NPR). Because of the NPR effect, stable Q-switched pulses with an average output power of 17.5 mW, a single pulse energy of 72.7 nJ, a repetition rate of 241 kHz, a pulse width of 466 ns and a signal to noise ratio (SNR) of 58.8 dB are obtained with 600 mW pump power. To the best of our knowledge, the SNR is the highest among all-fiber passively Q-switched Erbium-doped laser. The stability of this Erbium-doped fiber laser (EDFL) is also examined by monitoring the laser consecutively for 5 hours at the laboratory conditions.

An Optical Ray Tracing Method for Simulating Beam-Steering Effects during Laser Diagnostics in Turbulent Media

Yejun Wang and Waruna Kulatilaka

Doc ID: 285868 Received 30 Jan 2017; Accepted 12 Mar 2017; Posted 16 Mar 2017  View: PDF

Abstract: In most coherent spectroscopic methods used in gas-phase laser diagnostics, multiple laser beams are often focused and crossed at a specific location in space to form the probe region. The desired signal is then generated as a result of nonlinear interactions between the beams in this overlapped region. When such diagnostic schemes are implemented in practical devices having turbulent reacting flow fields with refractive index gradients, resulting beam steering can give rise to large measurement uncertainties. The objective of this work is to simulate beam-steering effects arising from pressure and temperature gradients in gas-phase media using an optical ray tracing approach. The ZEMAX OpticStudioTM software package is used to simulate beam crossing and uncrossing effects in the presence of pressure and temperature gradients, specifically the conditions present in high-pressure, high-temperature combustion devices such as gas turbine engines. Specific cases involving two-beam and three-beam crossing configurations are simulated. The model formulation, the effects of pressure and temperature gradients, and resulting beam-steering effects are analyzed. The results show that thermal gradients in the range of 300–3000 K have minimal effects, while pressure gradients in the range of 1–50 atm result in pronounced beam steering and resulting signal fluctuations in the geometries investigated. However, with increasing pressures, the temperature fluctuations can also have a pronounced effect on the resultant signal levels. 2017 Optical Society of America

A practical dual-band THz imaging system

Zhou Deliang, Liwei Hou, WEI XIE, YUANZHANG ZANG, BIN LU, Jian Chen, and Peiheng Wu

Doc ID: 282817 Received 16 Dec 2016; Accepted 10 Mar 2017; Posted 13 Mar 2017  View: PDF

Abstract: This paper introduces a dual-band terahertz (THz) imaging system as a potential product for nondestructive testing using heterodyne detectors and continuous-wave (CW) sources. The operating frequencies of the system are 110.4 and 220.8 GHz. Multi-band fusion technology combines the advantages of the greater spatial resolution of the high-frequency band and the enhanced sensitivity of the low-frequency band to improve the detection ability of the system. Additionally, the interference cancellation technology is used to obtain a superior image quality. The spatial resolution of this system was approximately 3 mm. The results show that the system can be used for bonding quality and embedded defect detection in radar domes and foam materials adhered to metal plates in aircrafts.

Non-Scanning Moiré Deflectometry for Measurement of Nonlinear Refractive Index and absorption coefficient of Liquids

shahrzad Shahrabi Farahani, Khosro Madanipour, and ata koohian

Doc ID: 283254 Received 20 Dec 2016; Accepted 10 Mar 2017; Posted 13 Mar 2017  View: PDF

Abstract: In this work, a non-scanning measurement technique is presented for determining the non-linear refractive index and absorption coefficient of liquid media based on Moiré deflectometry. In the proposed method two lasers are used: a low power, wide beam as probe and a high power with specific wavelength as pump. Interaction of pump laser beam with the nonlinear sample changes the refractive index which leads to change in convergence/divergence of the collimated incident probe laser beam. The induced deflection is monitored by Moiré deflectometry. If the pump laser has a Gaussian intensity profile, the refractive index profile of sample is Gaussian too. Measuring the deflection angle of the probe beam by Moiré fringes deflection, and using inverse Abel transform integral, the refractive index profile and so nonlinear refractive index can be determined. This method is fast, easy and insensitive to environmental noise and allows real time measurement. Also, the refractive index profile of the interacted medium with pump laser can be achieved by this technique. As a liquid sample, a DCJ dye in water solution was studied. The value of nonlinear refractive index, n2, and absorption coefficient, α, were obtained –2.54×10-4 cm2w-1 and 1.368cm-1 respectively.

Stimulated Emission in Aluminum Laser Induced Plasma: Experimental Study

Igor Gornushkin, Reto Glaus, and Lev Nagli

Doc ID: 282460 Received 24 Jan 2017; Accepted 10 Mar 2017; Posted 10 Mar 2017  View: PDF

Abstract: The stimulated emission (SE) in aluminum laser induced plasma pumped in resonance with the 3s p-3s24s aluminum transition at 266.04 nm is investigated experimentally. It is shown that the population inversion between the 3s p and 3s24s states can be created by weak pumping at several μJ - mJ pulse energies and result in high gain. The intensity of the SE at 396.15 nm is related to the number density of Al atoms via absorption measurements. It is found that the SE in forward and backward directions with respect to the pumping laser is different in terms of the line shape and intensity that is attributed to inhomogeneity in a gain coefficient across the plasma plume.

An integrated refractive index sensor using silicon slotwaveguides

Ka Li, Xue Feng, Kaiyu Cui, Wei Zhang, Fang Liu, and Yidong Huang

Doc ID: 284252 Received 09 Jan 2017; Accepted 09 Mar 2017; Posted 10 Mar 2017  View: PDF

Abstract: We have proposed an integrated refractive index (RI) sensor based on evanescent field absorption (EFA) withinsilicon slot waveguide, where the RI variation is translated into varied attenuation coefficient and eventually theoutput power at the end of waveguide. To demonstrate the operating principle of such RI-EFA sensor, a specificstructure is designed and discussed with numerical simulations. The calculated results indicate that the detectionlimit of our proposed RI-EFA sensor could be as good as ~10-8 RIU for homogeneous sensing and ~10-7 RIU forsurface sensing with optimized structural parameters at the wavelength of 1064nm. Since only straight slotwaveguide and optical power detection are required for our proposed sensor, we believe that it is promising toachieve an integrated and portable sensor on a single chip.

Dielectric V-ridge gratings: transition fromantireflection to retroreflection

gaurav bose, Ismo Vartiainen, Matthieu Roussey, Markku Kuittinen, Jani Tervo, and Jari Turunen

Doc ID: 284804 Received 13 Jan 2017; Accepted 09 Mar 2017; Posted 10 Mar 2017  View: PDF

Abstract: We present a systematic study of the optical properties of dielectric gratings with symmetric V-shapedridges having a 90° apex angle and refractive index n. Such structures exhibit completely different opticalproperties if the dimensions are scaled with respect to the vacuum wavelength λ₀ of light. In the subwavelengthdomain, where the grating period d is less than λ₀/n, the grating behaves as an antireflectionlayer. In the large-period domain d>> λ₀ (with normal incidence from the dielectric side) the gratingturns into a micro-retroreflector array. The transition between these well-known domains is studied usingrigorous diffraction theory. The results are verified experimentally by fabricating and characterizingV-profile gratings with the aid of wet etching of silicon using a process that defines a 90⁰ apex angle andreplication into a polymer.

Nonlinearity characterization of arrayspectroradiometers for the solar UV measurements

Tomi Pulli, Saulius Nevas, Omar Omar El Gawhary, Steven Van Den Berg, Janne Askola, Petri Karha, Farshid Manoocheri, and Erkki Ikonen

Doc ID: 286013 Received 01 Feb 2017; Accepted 09 Mar 2017; Posted 10 Mar 2017  View: PDF

Abstract: Array spectroradiometers are attractive alternatives to scanning spectroradiometers in solar ultravioletmeasurements. However, the measurement of solar spectral irradiance imposes stringent requirementsfor the linearity of the instruments. In this article, two array spectroradiometers were characterized fornonlinearity. Significant nonlinearities, in excess of 10 %, as a function of analog-to-digital convertercounts were discovered. Additional nonlinearities as a function of integration time were observed at verylong integration times. No clear residual nonlinearity as a function of spectral irradiance was witnesseddespite the characterization spanning four orders of magnitude of spectral irradiance. The characterizationswere carried out with three measurement setups, which are briefly compared.

Spectral characterization and discrimination ofsynthetic fibers with NIR hyperspectral imagingsystem

Xiaoke Jin, Hafeezullah Memon, wei tian, Qinli Yin, Xiaofang Zhan, and Chengyan Zhu

Doc ID: 281714 Received 29 Nov 2016; Accepted 09 Mar 2017; Posted 10 Mar 2017  View: PDF

Abstract: Synthetic fibers account for about half of all fiber usage with applications in every textile field. Whereas, thephenomenon of fiber composition not matching the label harms the consumer interests and impedes marketdevelopment. Hyperspectral imaging technology as a potential technique can be utilized to discriminate masssynthetic fibers rapidly, nondestructively and achieves the functions that traditional Fourier transform infraredinstrument does not have. On the basis of investigating the impact of dope-dyeing and wrapping processes onspectrums, the spectral features (from 900 to 2500 nm) of six categories of synthetic fibers were extracted withhyperspectral imaging system. A principal component analysis-linear discriminant analysis (PCA-LDA) model wasdeveloped to discriminate the chemical content of fibers in different colors and structures, which showed 100%discrimination accuracy. Results demonstrated the feasibility of hyperspectral imaging system in synthetic fiberdiscrimination. Therefore, this method offers a more convenient alternative for textile industry on-sitediscrimination.

Evaluation of Femtosecond laser damage to gold pulse compression gratings fabricated by magnetron sputtering and e-beam evaporation

leilei wang, Fanyu Kong, Zhilin Xia, jin yunxia, Haopeng Huang, Linxin Li, Junming Chen, cui yun, and jianda Shao

Doc ID: 281817 Received 02 Dec 2016; Accepted 09 Mar 2017; Posted 10 Mar 2017  View: PDF

Abstract: In this study, two kinds of Au-coated gratings (ACGs) with a period of 1740 lines/mm were fabricated and evaluated. For these ACG samples, magnetron sputtering and e-beam evaporation were used as the gold deposition process, and the samples had a bandwidth of at least 170 nm, with the -1st order diffraction efficiency exceeding 90% around the center wavelength of 800 nm. The 1-on-1 damage threshold of ACGs fabricated by magnetron sputtering and e-beam measured at a pulse width of 60 fs was 0.59 J/cm2 and 0.43 J/cm2 in the case of the normal beam, respectively. The typical damage morphology of the former type of samples was melting of the gold film, whereas those of the latter type were blisters and peeling off of the gold film. In theory, the electromagnetic field, temperature field, and thermal stress field distribution in the ACGs were calculated using the finite element method. We demonstrated that the adhesion between the gold film and the photoresist played an important role in determining the damage behavior. Thus, the laser resistance of ACG can be improved by enhancing the adhesion between the gold film and the photoresist, and magnetron sputtering was an alternative method to obtain ACG with much better adhesion. Based on the results, a 970 mm × 370 mm ACG was fabricated by magnetron sputtering.

Infrared Brewster-angle polarizing beam splitter using a high-index prism with small wedge angle

Rasheed Azzam

Doc ID: 287278 Received 22 Feb 2017; Accepted 09 Mar 2017; Posted 10 Mar 2017  View: PDF

Abstract: Specular reflection at the Brewster angle by a planar surface of a high-refractive-index transparent substrate is an effective means of generating linearly polarized light in the infrared. However, in such a reflection linear polarizer, the refracted light beam is usually dumped. In this Letter we describe a polarizing beam splitter (PBS) that uses a high-index prism with small wedge angle to generate two orthogonally p and s linearly polarized beams that travel in orthogonal directions. A single-layer antireflection coating (ARC) at the exit face of the prism can be embedded with aligned Ag nano needles to suppress the transmission of the small, residual, s-polarized refracted component. An example of such PBS, that uses a PbTe prism with ZnSe ARC in the mid-infrared, is presented.

A Novel Semi-Automated Localization of Dermal Epidermal Junction in OCT Images of Skin

ADELEH TAGHAVIKHALILBAD, Saba Adabi, anne clayton, hadi SOLTANIZADEH, DARIUS MEHREGAN, and Mohammad Avanaki

Doc ID: 282168 Received 05 Dec 2016; Accepted 08 Mar 2017; Posted 10 Mar 2017  View: PDF

Abstract: Identifying the location of the Dermal Epidermal Junction (DEJ) in skin images is essential in several clinicalapplications of dermatology such as epidermal thickness determination in healthy versus un-healthy skins, e.g., basalcell carcinoma (BCC). Optical coherence tomography (OCT) facilitates the visual detection of DEJ in-vivo. However, dueto the granular texture of speckle and a low contrast between dermis and epidermis, a skin border detection methodis required for DEJ localization. Current DEJ algorithms work well for skins with visible differentiable epidermal layerbut not for the skins of different body sites. In this paper, we present a semi-automated DEJ localization algorithmbased on graph theory for OCT images of skin. The proposed algorithm is performed in an interactive framework by agraphical representation of an attenuation coefficient map through a uniform-cost search method. For borderthinning, a fuzzy-based nonlinear smoothing technique is used. For evaluation, DEJ detection method is used byseveral experts and the results are compared with manual segmentation. The mean thickness error between theproposed algorithm and the experts’ opinion in Bland-Altman plot is computed as 14 μm; this is comparable to theresolution of the OCT. The results suggest that the proposed image processing method successfully detects DEJ.

A flexible global calibration of multi-camera with nonoverlappingfields-of-view using circular targets

Zheng Gong, zhen liu, and Guangjun Zhang

Doc ID: 280240 Received 07 Nov 2016; Accepted 08 Mar 2017; Posted 10 Mar 2017  View: PDF

Abstract: Global calibration of multi-camera systems is a difficult problem. The key is to find an appropriate calibrationtarget. This paper proposes a flexible method to construct a global calibration target with circular targets. Anyobject that is to be measured by the system can be used as a calibration target with the help of a hand-hold scanner.The calibration method does not need a special calibration target or multiple shots, which is flexible in applications.Circular targets pasted on the calibration target are used as features that are captured by cameras. The particleswarm optimization method is employed to correct the eccentricity error in the projection of circular targets. Theeccentricity correction method does not need any prior knowledge except camera intrinsic parameters. A syntheticdata experiment was performed to validate the eccentricity correction method and a physical experiment in a trainwheelset inner-side distance measurement system was performed to validate the global calibration method. Themeasurement accuracy of the system was better than 0.1mm, and the eccentricity correction method improved the3D reconstruction accuracy by about 0.1mm.

Nonimaging polygonal mirrors achieving uniform irradiance distributions on CPV cells

Max Schmitz, Fabian Dähler, François Elvinger, Andrea Pedretti, and Aldo Steinfeld

Doc ID: 284019 Received 05 Jan 2017; Accepted 07 Mar 2017; Posted 08 Mar 2017  View: PDF

Abstract: We introduce a design methodology for nonimaging, single-reflection mirrors with polygonal inlet apertures that generate a uniform irradiance distribution on a polygonal outlet aperture, enabling a multitude of applications within the domain of concentrated photovoltaics. Notably, we present single-mirror concentrators of square and hexagonal perimeter that achieve very high irradiance uniformity on a square receiver at concentrations ranging from 100 to 1000 suns. These optical designs can be assembled in compound concentrators with maximized active area fraction by leveraging tessellation. More advanced multi-mirror concentrators, where each mirror individually illuminates the whole area of the receiver, allow for an improved performance while permitting greater flexibility for the concentrator shape and robustness against partial shading of the inlet aperture.

Cr:ZnS saturable absorber passively Q-switched mode-locking Tm,Ho:LLF laser

Xinlu Zhang, Yong Luo, Tianhan Wang, Junfeng Dai, Jianxin Zhang, Jiang Li, cui jinhui, and Jinjer Huang

Doc ID: 284041 Received 06 Jan 2017; Accepted 07 Mar 2017; Posted 08 Mar 2017  View: PDF

Abstract: We first report on the diode-end-pumped passively Q-switched mode-locking Tm,Ho:LLF laser at 2053 nm by using a Cr:ZnS saturable absorber. Stable Q-switched mode-locking pulse train with a nearly 100% modulation depth was achieved. The repetition frequency of the Q-switched pulse envelope increased from 0.5 to 12.3 kHz with increasing pump power from 1 to 4.36 W. The maximum average output power of 145 mW was obtained, and the width of the mode-locked pulse was estimated to be less than 682 ps with a 250 MHz repetition frequency within a Q-switched pulse envelope of about 700 ns.

Two Stage Innoslab-Amplifier for Energy Scaling from 100 mJ to >500 mJ for Future Lidar Applications

Michael Strotkamp, Florian Elsen, Jens Loehring, Martin Traub, and Dieter Hoffmann

Doc ID: 284723 Received 13 Jan 2017; Accepted 07 Mar 2017; Posted 08 Mar 2017  View: PDF

Abstract: A Nd:YAG-MOPA system consisting of a stable oscillator and two subsequent Innoslab-based amplifier stages has been designed and built as a technology demonstrator for future lidar applications. Overall, the authors could demonstrate that it generates more than 500 mJ of pulse energy at 1064 nm wavelength and 100 Hz pulse repetition frequency at about 30 ns pulse duration in single longitudinal mode. Seeded with 75 mJ pulses, the 2nd amplifier stage achieved an optical efficiency (extracted energy to pump energy) of more than % while preserving excellent beam quality. To address the 500 mJ regime while retaining the basic system properties, an established Innoslab design was scaled geometrically.

Experimental study of temporal-spatial binary pattern projection for 3D shape acquisition

Pei Zhou, Jiangping Zhu, Xianyu Su, Zhisheng You, Hailong Jing, Cao Xiao, and Min Zhong

Doc ID: 284896 Received 17 Jan 2017; Accepted 07 Mar 2017; Posted 08 Mar 2017  View: PDF

Abstract: Three dimension (3D) acquisition of an object with modest accuracy and speed is of particular concern in practice. The performance of digital sinusoidal pattern projection using off-the-shelf digital video projector is generally discounted by the nonlinearity and low switch rate. In this paper, a binary encoding method to encode one computer-generated standard sinusoidal pattern is presented for circumventing such deficiencies. In previous work (Opt. Eng. 54(5), 054108-054108(2015)), we have developed a 3D system on basis of this encoding tactic and showed its application prospect. Here, we first build a physical model to explain the mechanism how to generate good sinusoidality. The phase accuracy with respect to conventional spatial binary encoding method and sinusoidal pattern is also comparatively evaluated through simulation and experiments. We also adopt two phase-height mapping relationships to experimentally compare the measurement accuracy amongst them. The results indicate that, the proposed binary encoding strategy has a comparable performance to that of sinusoidal pattern projection and enjoy some advantages over spatial binary method under same conditions.

Wideband and Multi-Frequency Infrared Cloaking ofSpherical Objects by Using Graphene BasedMetasurface

Nosrat Granpayeh, Elnaz Shokati, and Mohammad Danaeifar

Doc ID: 285197 Received 19 Jan 2017; Accepted 07 Mar 2017; Posted 08 Mar 2017  View: PDF

Abstract: The ultrathin graphene metasurface is proposed as a mantle cloak to achieve wideband tunable scatteringreduction around the spherical (three-dimensional) objects. The cloaking shell over metallic or dielectric sphere isstructured by periodic array of graphene nanodisks that operate at infrared frequencies. By using thepolarizability of the graphene nanodisks and equivalent conductivity method, the metasurface reactance isobtained. To achieve cloaking shell for both dielectric and conducting spheres, the metasurface reactance as afunction of nanodisks dimensions, graphene’s Fermi energy, and permittivity of the surrounding areas can betuned from inductive to capacitive situation. Inhomogeneous metasurfaces including graphene nanodisks withdifferent radii provide wideband invisibility due to extra resonances. We could significantly increase the 3-dBbandwidth more than the homogenous case by simpler realistic designs compared to the multilayer structures. Theanalytical results are confirmed with full-wave numerical simulations.

Surface structural damage study in cortical bone due medical drilling

César Giovani Tavera Ruiz, Manuel De la Torre I., Jorge Flores, Maria Hernandez Montes, Fernando Mendoza-Santoyo, Manuel de Jesus Briones-Reyes, and Jorge Sanchez-Preciado

Doc ID: 281990 Received 05 Dec 2016; Accepted 07 Mar 2017; Posted 08 Mar 2017  View: PDF

Abstract: A bone’s fracture could be produced by an excessive, repetitive or sudden load. A regular medical practice to heal it is to fix it in two possible ways: external immobilization, using a ferule, or an internal fixation, using a prosthetic device commonly attached to the bone by means of surgical screws. The bone’s volume loss due to this drilling modifies its structure either in the presence or absence of a fracture. In order to observe the bone’s surface behavior caused by the drilling effects, a digital holographic interferometer is used to analyze the displacement surface’s variations in non-fractured post mortem porcine femoral bones. Several non-drilled post mortem bones are compressed and compared with a set of post mortem bones with different number of cortical drillings. During each compression test, a series of digital interferometric holograms were recorded using a high speed CMOS camera. The results are presented as pseudo 3D mesh displacement maps for comparisons in the physiological range of load (30 and 50lbs) and beyond (100, 200 and 400lbs). The high resolution of the optical phase gives a better understanding about the bone’s micro structural modifications. Finally, a relationship between compression load and bone volume loss due to the drilling was observed. The results prove that Digital Holographic Interferometry is a viable technique to study the conditions that avoid the surgical screw from loosening in medical procedures of this kind.

Visualizing Spatiotemporal Pulse Propagation: First-Order Spatiotemporal Couplings in Laser Pulses

Michelle Rhodes, Zhe Guang, Rick Trebino, and Jerrold Pease

Doc ID: 283099 Received 19 Dec 2016; Accepted 06 Mar 2017; Posted 08 Mar 2017  View: PDF

Abstract: Even though a general theory of first-order spatiotemporal couplings exists in the literature, it is often difficult to visualize how these distortions affect laser pulses. In particular, it is difficult to show the spatiotemporal phase of pulses in a meaningful way. Here we propose a general solution to plotting the electric fields of pulses in 3D space that intuitively shows the effects of spatiotemporal phase. The temporal phase information is color-coded using spectrograms and color response functions, and the beam is propagated to show the spatial phase evolution. Using this plotting technique, we generate 2D and 3D images and movies that show the effects of spatiotemporal couplings.

Simplified projection technique to correctgeometric and chromatic lens aberrationsusing plenoptic imaging

Xavier Dallaire and Simon Thibault

Doc ID: 285759 Received 27 Jan 2017; Accepted 06 Mar 2017; Posted 08 Mar 2017  View: PDF

Abstract: Plenoptic imaging has been used in the past decade mainly for 3D reconstruction or digital refocusing. It was alsoshown that this technology has potential for correcting monochromatic aberrations in a standard optical system. Inthis paper, we present an algorithm for reconstructing images using a projection technique while correctingdefects present in it that can apply to chromatic aberrations and wide-angle optical systems. We show that theimpact of noise on the reconstruction procedure is minimal. Trade-offs between the sampling of the optical systemneeded for characterization and image quality are presented. Examples are shown for aberrations in a classicoptical system and for chromatic aberrations. The technique is also applied to a wide-angle (FFOV 140°) opticalsystem. This technique could be used in order to further simplify or minimize optical systems.

Sensitivity Study of X-ray Luminescence Computed Tomography

Michael Lun, Wei Zhang, and Changqing Li

Doc ID: 286048 Received 02 Feb 2017; Accepted 06 Mar 2017; Posted 10 Mar 2017  View: PDF

Abstract: X-ray luminescence computed tomography (XLCT) is a hybrid molecular imaging modality that combines the merits of both x-ray imaging (high resolution) and optical imaging (high sensitivity). In this study, we have evaluated the sensitivity of XLCT with phantom experiments by scanning targets of different phosphor concentrations at different depths. We found that XLCT is capable of imaging targets of very low concentrations (27.6 µM) at significant depths, such as 21 mm. Our results demonstrate that there is little variation in the reconstructed target size with a maximum target size error of 4.35 % for different imaging depths for XLCT. We have for the first time, compared the sensitivity of XLCT with that of traditional computed tomography (CT) for phosphor targets. We found that XLCT’s use of x-ray induced photons provides much higher measurement sensitivity and contrast compared to CT which provides image contrast solely based on x-ray attenuation.

Nonlinear adiabatic optical isolator

Andon Rangelov and Stefano Longhi

Doc ID: 283246 Received 21 Dec 2016; Accepted 05 Mar 2017; Posted 08 Mar 2017  View: PDF

Abstract: We theoretically propose a method for optical isolation based on adiabatic nonlinear sum frequency generation in a chirped quasi-phase-matching crystal with strong absorption at the generated sum frequency wave. The method does not suffer from limitations of dynamic reciprocity found in other nonlinear optical isolation methods, and can provide tunable optical isolation with ultrafast all-optical switching capability. Moreover, as an adiabatic technique it is robust to variations in the optical design and is relatively broadband.

The effect of thermally induced birefringence onperformance of KD*P electro-optics crystal withrectangular shape

Xingliang Yin, Menghua Jiang, zhe sun, yongling hui, hong lei, and Qiang Li

Doc ID: 281752 Received 29 Nov 2016; Accepted 05 Mar 2017; Posted 06 Mar 2017  View: PDF

Abstract: In this paper, we present the first demonstration of a new rectangular KD*P crystal as an electro-optic switch andcalculations of the stress-induced birefringence and depolarization loss in the crystal. We simulated and experimentallydemonstrated the thermal depolarization loss of crystal in both cylindrical and rectangular shape. The results show thatusing rectangular KD*P crystal, the effects of the thermal induced birefringence and depolarization can be lessened.

Dielectric properties of CsPbBr3 quantum dotssolution in terahertz region

Dongsheng Yang, Xiang'ai Cheng, Yu Liu, chao shen, Zhongjie Xu, Xin Zheng, and Tian Jiang

Doc ID: 284527 Received 10 Jan 2017; Accepted 05 Mar 2017; Posted 06 Mar 2017  View: PDF

Abstract: In recent years, CsPbBr3 quantum dots (QDs) have attracted great attention due to their bright prospect insolar cell studies. Dielectric properties are important for the fabrication of optoelectronic devices. Here,dielectric properties of CsPbBr3 QDs solution are investigated between 0.1 THz and 2.0 THz by terahertz timedomainspectroscopy (THz-TDS). The frequency dependent transmitted ratio is measured to decrease from0.96 to 0.80 in this range. By comparison of the different concentrations of QDs solution, the frequencyaveraged absorption is linear increased with the increase of QDs concentration. After that, frequencydependent dielectric constant including complex refractive index, complex dielectric constant andconductivity are extracted by Fourier transforms of the time-domain spectrum. An effective mediumapproach (EMA) method is adopted to extract the complex dielectric constant of CsPbBr3 QDs inclusion and aslight peak around 0.4 THz is found in the imaginary part of the dielectric constant. The result of Drude-Lorentz fitting shows the phonon plays a dominate role on the dielectric properties of CsPbBr3 QDs solution.Moreover, the THz response of CsPbBr3 QD is found unchanged when the test is conducted under illumination.We attribute this phenomenon to the discrete energy level of excitons in CsPbBr3 QDs due to quantumconfinement and design a comparative experiment to validate it. This study is significant for deeper insight ofthe dielectric properties of CsPbBr3 QDs and thus is helpful to its applications in optoelectronics.

Quality assessment of refocus criteria for particleimaging in digital off-axis holography

Pascal Picart, Larbi Bouamama, Derradji Bahloul, and Soumaya Kara

Doc ID: 281944 Received 01 Dec 2016; Accepted 04 Mar 2017; Posted 08 Mar 2017  View: PDF

Abstract: This paper proposes a quality assessment of focusing criteria for imaging in digital off-axis holography. Inliterature, several refocus criteria have been proposed in the past to get the best refocus distance in digitalholography. As a general rule, the best focusing plane is determined by the reconstruction distance for which thecriterion function presents a maximum or a minimum. To evaluate the robustness of these criteria, a set of thirteencriteria is compared with application on both amplitude and phase objects from off-axis holographic data.Simulation and experimental results lead to define general rule and to exhibit the most robust criteria for accurateand rapid refocusing in digital holography.

Real object pickup method of integral imaging using offset lens array

Junkyu Yim, KiHong Choi, and Sung-Wook Min

Doc ID: 279417 Received 25 Oct 2016; Accepted 03 Mar 2017; Posted 03 Mar 2017  View: PDF

Abstract: We propose the pickup system of integral imaging using the offset lens array which is the useful optical component for the both pickup and display processes. The main purpose of our system is resolving the pseudoscopic image problem of integral imaging. Also, the flipped image of integral imaging which has the wrong perspective information can be removed by adding the external barrier in the display process. In this paper, the above properties are explained in detail and the experimental results to verify the feasibility of the proposed system are presented. We certain that our system can also applied to other various pickup systems based on integral imaging.

Advanced image analysis verifies geometry performance of micro-milling systems

Bita Daemi, Peter Ekberg, and Lars Mattsson

Doc ID: 281759 Received 29 Nov 2016; Accepted 02 Mar 2017; Posted 03 Mar 2017  View: PDF

Abstract: Accurate dimensional measurement of micro-milled items is a challenge and machine specifications do not include operational parameters in the workshop. Therefore, a verification test that shows the machine’s overall geometrical performance over its working area would help machine users in the assessment and adjustment of their equipment. In this study we present an optical technique capable of finding micro milled features at submicron uncertainty over working areas >10 cm2. The technique relies on an ultra-precision measurement microscope combined with advanced image analysis to get the center of gravity of milled cross shaped features at subpixel levels. Special algorithms had to be developed to handle the disturbing influence of burr and milling marks. The results show repeatability, reproducibility and axis straightness for three micro-milling facilities and also discovered an unknown 2 μm amplitude undulation in one of them.

Miniaturized photogenerated electro-optic axicon lensGaussian-to-Bessel beam conversion

Giuseppe Di Domenico, Jacopo Parravicini, Giuseppe Antonacci, Salvatore Silvestri, Ronny Agranat, and Eugenio Del Re

Doc ID: 282882 Received 15 Dec 2016; Accepted 02 Mar 2017; Posted 03 Mar 2017  View: PDF

Abstract: We experimentally demonstrate an electro-opticGaussian-to-Bessel beam-converter miniaturized downto a 30 30 mm pixel in a KLTN paraelectric crystal.The converter is based on the electro-optic activation ofa photoinduced and reconfigurable volume axicon-lensachieved using a pre-written photorefractive funnelspace-charge distribution. The transmitted light beamhas a tunable depth of field that can be more than twicethat of a conventional beam with the added feature ofbeing self-healing.

Versatile dispersion characteristics of water solution of glycerine in selective filling of holes in photonic crystal fibers

prasenjt ghosh and Somenath Sarkar

Doc ID: 281616 Received 30 Nov 2016; Accepted 02 Mar 2017; Posted 06 Mar 2017  View: PDF

Abstract: Using water solution of glycerine with various concentrations, we investigate the dispersion characteristics of photonic crystal fibers by selective filling of holes. Our analysis is based on a simple but accurate semi-vectorial solution of Helmholtz’s equation by the finite difference method devised with a mode–field convergence technique and crosschecked by results with those from a, deeply involved, multipole method. Significantly, a better ultra-flatness but near zero group velocity dispersion is revealed with 20 % water solution of glycerine superior to pure water of a very recent case when the holes of the first ring of the fiber are filled. This versatile effect in management of holes of identical diameter with liquid is expected to play a guiding role in studies of supercontinuum generation.

MDGC performance evaluation method for gas leakinfrared imaging detection systems

Zhang Xu, Weiqi Jin, jiakun Li, Xia Wang, and Shuo Li

Doc ID: 280513 Received 23 Nov 2016; Accepted 01 Mar 2017; Posted 02 Mar 2017  View: PDF

Abstract: Thermal imaging technology is an effective means of detecting hazardous gas leaks. Much attention has been paidto evaluation of the performance of gas leak infrared imaging detection systems due to several potentialapplications. The MRTD (minimum resolvable temperature difference) and the MDTD (minimum detectabletemperature difference) are commonly used as the main indicators of thermal imaging system performance. Thisarticle establishes the MDGC (minimum detectable gas concentration) performance evaluation model based on thedefinition and derivation of MDTD. We proposed the direct calculation and equivalent calculation method of MDGCbased on the MDTD measurement system. We build an experimental MDGC measurement system, which indicatesthe MDGC model can describe the detection performance of thermal imaging system to typical gases. The directcalculation, equivalent calculation and direct measurement results are consistent. The MDGC and the MRGC(minimum resolvable gas concentration) model can effectively describe the performance of “detection” and“spatial detail resolution” of thermal imaging systems to gas leak, respectively, constitute the main performanceindicators of gas leak detection systems.

Polarization-anisotropy of thermal lens in Yb:KY(WO₄)₂ laser crystal under high-power diode pumping

Pavel Loiko, Sujith Manjooran, Konstantin Yumashev, and Arkady Major

Doc ID: 285702 Received 30 Jan 2017; Accepted 28 Feb 2017; Posted 03 Mar 2017  View: PDF

Abstract: Thermal lensing was studied in an Ng-cut monoclinic Yb:KY(WO₄)₂ (Yb:KYW) laser crystal under high-power diode pumping at ~980 nm, for the two principal light polarizations, E || Nm and E || Np. For both polarizations, thermal lens (TL) was positive. It was found that operation of an Yb:KYW laser with the E || Np polarization corresponds to a weaker TL that results in a better quality of the laser beam and superior power scaling capabilities. The sensitivity factors of the TL in this case were M = 0.37 and 0.57 m-1/W for the mg and pg principal meridional planes, respectively, and the astigmatism degree was as low as S/M = 35% (for a pump beam radius of wp =175 μm). The photo-elastic terms, fractional heat loading and generalized thermo-optic coefficients were evaluated.

Second harmonic generation of a dual-frequency laserin a MgO:PPLN crystal

Suhui Yang, Ying Kang, Brunel Marc, Lijun Cheng, Changming Zhao, and Haiyang Zhang

Doc ID: 283469 Received 22 Dec 2016; Accepted 27 Feb 2017; Posted 01 Mar 2017  View: PDF

Abstract: A dual frequency CW laser at a wavelength of 1.064μm is frequency doubled in a MgO:PPLN nonlinear crystal. Thefundamental dual frequency laser has a tunable beat note from 125 MHz to 175 MHz. A laser-diode pumped fiberamplifier is used to amplify the dual frequency fundamental output to a maximum power of 50 W before frequencydoubling. The maximum output power of the green light is 1.75 W when the input fundamental power is 12 W,corresponding to a frequency doubling efficiency of 14.6%. After frequency doubling, green light with modulationfrequencies in two bands from 125-175 MHz and 250-350 MHz is achieved simultaneously. The relative intensitiesof the beat notes at the two bands can be adjusted by changing the relative intensities at different frequencies ofthe fundamental light. The spectral width and frequency stabilities of the beat notes in fundamental wave andgreen light are also measured respectively. The modulated green light has potential applications in under waterranging, communication and imaging.

The research on partially coherent flat-topped vortex hollow beams propagation in turbulent atmosphere

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

Doc ID: 284446 Received 10 Jan 2017; Accepted 24 Feb 2017; Posted 01 Mar 2017  View: PDF

Abstract: In this paper, the aperture averaged scintillation, mean signal-to-noise (SNR) and average bit error rate (BER) for the partially coherent flat-topped vortex hollow beams propagating in turbulent atmosphere are evaluated. The variation of the aperture averaged scintillation against the coherence length of the beams and size of the receiver aperture is studied. It is also found that the aperture averaged scintillation increases with the topological charge of the partially coherent flat-topped vortex hollow beams. The partially coherent flat-topped vortex hollow beam with the smaller beam order has advantage to resist the effect of the turbulence. Investigation are also made illustrating the variation of the mean SNR and average BER against the coherence length.

Phase-matching properties of BaGa₄Se₇ for SHG and SFG in the 0.901-10.5910 μm range

Kiyoshi Kato, Kentaro Miyata, and Valentin Petrov

Doc ID: 285401 Received 23 Jan 2017; Accepted 24 Feb 2017; Posted 01 Mar 2017  View: PDF

Abstract: We report new experimental results on the phase-matching properties of a BaGa₄Se₇ crystal for harmonic generation of a Nd:YAG laser-pumped AgGaS₂ optical parametric oscillator (OPO) and a CO₂ laser in the 0.901-10.5910 µm range. In addition, we present new Sellmeier equations that provide a good reproduction of the present experimental results as well as the published data points for Nd:YAG laser-pumped OPO and optical parametric amplifier (OPA) in the 3.10-15.22 μm range and a Ho:YAG laser-pumped OPA in the 3.49-5.18 μm range.

Compact, high power, high beam quality quasi-CWmicrosecond five-pass zigzag slab 1319 nm amplifier

Chuan Guo, Junwei Zuo, Qi Bian, Chang Xu, Qingshuang Zong, Bo Yong, yu shen, ZONG Nan, Gao Wei, Yanyong Lin, Yuan Lei, yang liu, Da Cui, qinjun peng, and Zuyan Xu

Doc ID: 285226 Received 19 Jan 2017; Accepted 24 Feb 2017; Posted 03 Mar 2017  View: PDF

Abstract: We demonstrate a compact high power quasi-continuous-wave (QCW) end-pumped 1319 nm Nd:YAG slabamplifier laser with good beam quality simultaneously. The laser is based on a QCW pulse Nd:YAG masteroscillator and a Nd:YAG slab amplifier with multi-pass Zigzag architecture. The amplifier operates at a pulserepetition frequency of 500 Hz and pulse width of ~105 μs, delivering a maximum output power of 51.5Wunder absorbed pump power of 217.8 W, corresponding to an extraction efficiency of 14.2%. The beamquality factor is measured to be 􀡹􀢞􀫛 = 1.61 and 􀡹􀢟 􀫛= 1.81 in the orthogonal directions. To the best of ourknowledge, this is the first compact high power high beam quality QCW Nd:YAG amplifier at 1319 nm based ona multi-pass Zigzag slab structure.

Self calibration for lensless color microscopy

Olivier Flasseur, Corinne Fournier, Nicolas Verrier, Loïc Denis, Frederic Jolivet, Anthony Cazier, and Thierry Lepine

Doc ID: 281955 Received 05 Dec 2016; Accepted 23 Feb 2017; Posted 01 Mar 2017  View: PDF

Abstract: Lensless microscopy, in-line digital and color holography are recent quantitative 3D imaging methods used in several areas including biomedical imaging and microfluidics. However, with cost effective and compact designs, the wavelengths of the sources are only imprecisely known mainly due to their temperature dependence. In addition, most color sensors come with a Bayer color filter array. The lack of precision on the wavelengths can lead to errors during the reconstruction step. The spectral width of the Bayer filter results in a mixture of signals recorded on each color channel (spectral crosstalk) which is also an error source. We propose to use a parametric inverse problem approach to achieve the self-calibration of a digital color holography setup. This process enables estimation of wavelengths (with a narrower or similar range of uncertainty as the typical ranges provided by the manufacturer) plus accurate estimation of crosstalk. We show that taking the crosstalk phenomenon into account in the reconstruction step improves its accuracy.

Considerations on the proposed linear theory of surface measurement for coherence scanning interferometers

Andrew Henning and Claudio Giusca

Doc ID: 270137 Received 11 Jul 2016; Accepted 22 Feb 2017; Posted 22 Feb 2017  View: PDF

Abstract: It was suggested in [Appl. Opt, 52, pp.3662, (2013)] that the result of a measurement {\it{via}} Coherence Scanning Interferometry could be viewed as the convolution of a Point Spread Function of the instrument and an open surface in 3 dimensional space that lies at the air/material interface over a portion of the object's surface. Further, it was suggested that by measuring certain objects, such as ones that are very close to spherical, and whose surface is known to a sufficient level of accuracy, then a Point Spread Function for the instrument could be determined from the measurement result. We conclude that the approximations used in this calculation do not give sufficient accuracy to allow this to be achieved, and that the truncation of the surface function from the closed surface surrounding the object is not defined sufficiently well in order to give unique solution to the problem, and therefore cannot be correct in its current form. The physical justification for the truncation of the surface in this manner is also questioned.

The optimization and continuous fabrication of motheyenanostructure array on flexible PET substratetowards broadband antireflection

Chengpeng Zhang, Peiyun Yi, Linfa Peng, Xinmin Lai, and Jun Ni

Doc ID: 282526 Received 08 Dec 2016; Accepted 16 Feb 2017; Posted 16 Feb 2017  View: PDF

Abstract: Reflection loss can cause harmful effects on the performance of optoelectronic devices, such as cell phones, notebooks,displays, solar cells and light-emitting-diode (LED) devices. In order to obtain broadband antireflection (AR) properties,many researchers have utilized surface texture techniques to produce antireflection subwavelength structures on theinterfaces. Among the antireflection subwavelength structures, the moth-eye nanostructure is one of the most promisingstructures with potential for commercialization in the near future. In this research, to obtain broadband AR performance,the optimization of moth-eye nanostructures was firstly carried out using the finite difference time domain (FDTD) methodwithin the spectral ranges of 400-800 nm, including the optimization of shape, height, pitch, and residual layer thickness. Inaddition, the continuous production of moth-eye nanostructure array upon a flexible PET substrate was demonstrated byusing roll-to-roll ultraviolet nanoimprint lithography (R2R UV-NIL) process and Anodic Aluminum Oxide (AAO) mold, whichprovided a solution for the cost-effective fabrication of moth-eye nanostructure array. The AR performance of moth-eyenanostructure array obtained by R2R UV-NIL process was also investigated experimentally and good consistence wasshown with the simulated results. This research can provide a beneficial direction for the optimization and cost-effectiveproduction of the moth-eye nanostructure array.

Infrared absorption spectrometer for the determination of temperature and species profiles in an entrained flow gasifier

Patrick Nau, Peter Kutne, Georg Eckel, Wolfgang Meier, Christian Hotz, and Sabine Fleck

Doc ID: 280604 Received 16 Nov 2016; Accepted 15 Feb 2017; Posted 09 Mar 2017  View: PDF

Abstract: An absorption spectrometer utilizing a tunable distributed feedback diode laser at 2.3 µm and an interband cascade laser at 3.1 µm has been developed to measure temperature and concentrations of CO, CH4, C2H2 and H2O under gasification conditions. A wavelength division multiplexing approach using a single ZrF4-fiber was used to measure both wavelength regions simultaneously. The performance of the spectrometer has been tested in laminar flat flames and a heated cell and then applied for measurements at an atmospheric entrained flow gasifier (REGA). A water cooled optical probe was used to provide optical access at two measurement positions. By moving the burner, axial profiles of temperature and species concentration could be obtained. These profiles were compared with numerical simulations and can be used to validate the simulation.

Interference filter tilting to detect a polycyclic aromatic hydrocarbon at the second harmonic of wavelength modulation frequency

Dmitri Lanevski, Koit Mauring, and Eric Tkaczyk

Doc ID: 282295 Received 07 Dec 2016; Accepted 07 Feb 2017; Posted 14 Mar 2017  View: PDF

Abstract: We present a practical implementation of the wavelength-modulation spectroscopy technique with second-harmonic detection (WMS-2f) for selective detection and concentration measurements of polycyclic aromatic hydrocarbons (PAHs) - common fossil fuel pollutants. The method is based on excitation light wavelength modulation around the maximum of a narrow peak in the absorption spectrum of a PAH and lock-in detection of fluorescence at the second harmonic of the excitation wavelength modulation frequency. A violet LED is used as the excitation source and wavelength modulation is performed via narrow-band interference filter tilting. Feasibility is demonstrated with a carcinogenic PAH, benzo(k)fluoranthene. Model computations are presented to estimate the influence of background signal on the sensitivity of the method.

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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