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Accepted papers to appear in an upcoming issue

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

Full Field Parallel Interferometry Coherence Probe Microscope for High Speed Optical Metrology

Ibrahim Abdulhalim and Avner Safrani

Doc ID: 231783 Received 26 Jan 2015; Accepted 04 May 2015; Posted 04 May 2015  View: PDF

Abstract: Parallel detection of several achromatic phase shifted images is used to obtain high speed high resolution full field optical coherence probe tomography system based on polarization interferometry. The high enface imaging speed, the short coherence gate and high lateral resolution provided by the system are exploited to determine micro-bumps height uniformity in an integrated semiconductor chip at 50 frames per second. The technique is demonstrated using the Linnik microscope however it can be implemented on any polarization based interference microscopy system.

Measuring and modelling the inconspicuous iridescence of Formosan blue magpie’s feather (Urocissa caerulea)

Cheng-Chung Lee, Shih-Fang Liao, and Chun-Yang Yao

Doc ID: 232587 Received 14 Jan 2015; Accepted 04 May 2015; Posted 04 May 2015  View: PDF

Abstract: The iridescence of the blue feathers of the Formosan blue magpie (Urocissa caerulea) is not conspicuous when the viewing angle is less than 40°. The spongy medullary keratin inside the feather barbs is investigated by two-dimensional Fourier analysis of transmission electron microscopic images of various positions on a barb to explain this unique characteristic. The orientation of the quasi-ordered nanostructure varies depending on its position of the feather barb. The predicted reflectance increases with the distance of the nanostructures from the vertex of the feather barb, and this results agrees closely with measurements.

First machined immersion grating with theoretically-predicted diffraction efficiency

Yuji Ikeda, Naoto Kobayashi, Yuki Sarugaku, TAKASHI SUKEGAWA, Shigeru Sugiyama, Sayumi Kaji, Kenshi Nakanishi, Sohei Kondo, Chikako Yasui, Hirokazu Kataza, Takao Nakagawa, and Hideyo Kawakita

Doc ID: 233782 Received 05 Feb 2015; Accepted 04 May 2015; Posted 04 May 2015  View: PDF

Abstract: An immersion grating composed of a transmissive material with high refractive index (n>2) is a powerful device for high-resolution spectroscopy in the infrared region. Although this idea dates back more than 60 years, an immersion grating with high diffraction efficiency has never been realized due to difficulty in processing infrared crystals that are mostly brittle. While anisotropic etching is one successful method for fabricating a fine groove pattern on infrared crystal, machining is necessary for realizing any required blaze and apex angles. In this paper, we report the realization of the first-machined immersion grating, which is made of single crystal CdZnTe (CZT), with a high diffraction efficiency that is almost identical to that theoretically predicted by rigorous coupled-wave analysis (RCWA).

Fast and accurate focusing analysis of large photon sieve using pinhole ring diffraction model

Tao Liu, Xin Zhang, Jizhen Zhang, Yanxiong Wu, Hemeng Qu, and Lingjie Wang

Doc ID: 233834 Received 05 Feb 2015; Accepted 04 May 2015; Posted 04 May 2015  View: PDF

Abstract: In this paper, we developed a pinhole ring diffraction model for the focusing analysis of large photon sieve. Instead of analyzing individual pinholes, the focusing of all of the pinholes in a single ring zone is discussed. Explicit equation for the diffracted field of individual pinhole ring has been proposed. The validity range of this generalized model is investigated and the sufficient conditions for the validity of this pinhole ring diffraction model are analytically described. A practical example has been given and investigation reveals the high accuracy of the pinhole ring diffraction model. This simulation method could be used for the fast and accurate focusing analysis of large photon sieve.

Diffraction in volume reflection gratings with variable fringe contrast

David Brotherton-Ratcliffe, Hans Bjelkhagen, Ardie Osanlou, and Peter Excell

Doc ID: 234225 Received 09 Feb 2015; Accepted 04 May 2015; Posted 04 May 2015  View: PDF

Abstract: The PSM model is used to analyze the process of diffraction occurring in volume reflection gratings in which fringe contrast is an arbitrary function of distance within the grating. General analytic expressions for diffraction efficiency at Bragg resonance are obtained for unslanted panchromatic lossless reflection gratings. These formulae are then checked, for several diverse fringe contrast profiles with numerical solutions of the Helmholtz equation where exceptionally good agreement is observed. Away from Bragg resonance the case of the hyperbolically decaying fringe contrast profile is shown to lead to an analytic expression for the diffraction efficiency and this is again compared successfully with numerical solutions of the Helmholtz equation.

Computational Expressions for Signals in Frequency-Modulation Spectroscopy

Michael Di Rosa and Matthew Reiten

Doc ID: 234989 Received 19 Feb 2015; Accepted 03 May 2015; Posted 04 May 2015  View: PDF

Abstract: General expressions for the signals in frequency-modulation spectroscopy (FMS) appear in the literature but are often reduced to simple analytical equations following the assumption of a weak modulation index. This is little help to the experimentalist who wants to predict signals for modulation depths on the order of unity or greater, where strong FMS signals reside. Here, we develop general formulas for FMS signals in the case of an absorber with a Voigt line shape and then link these expressions to an example and existing numerical code for the line shape. The resulting computational recipe is easy to implement and exercised here to show where the larger FMS signals are found over the coordinates of modulation index and modulation frequency. One can also estimate from provided curves the in-phase FMS signal over a wide range of modulation parameters at either the Lorentzianbroadening or Doppler-broadening limit, or anywhere between by interpolation.

Real-time microscopic phase-shifting profilometry

Sam Van der Jeught, Joris Dirckx, and Joris Soons

Doc ID: 231325 Received 07 Jan 2015; Accepted 02 May 2015; Posted 04 May 2015  View: PDF

Abstract: A real-time microscopic profilometry system based on digital fringe projection and parallel programming has been developed and experimentally tested. Structured light patterns are projected onto an object through one pathway of a stereoscopic operation microscope. The patterns are deformed by the shape of the object and are then recorded with a high-speed CCD camera placed in the other pathway of the microscope. As the optical pathways of both arms are separated and reach the same object point at a relative angle, the recorded patterns allow the full-field object height variations to be calculated and the three-dimensional shape to be reconstructed by employing standard triangulation techniques. Applying proper hardware triggering, the projector-camera system is synchronized to capture up to 120 unique deformed line patterns per second. Using standard 4-step phase shifting profilometry techniques and applying graphics processing unit programming for fast phase wrapping, scaling and visualization, we demonstrate the capability of the proposed system to generate 30 microscopic height maps per second. This allows the qualitative depth perception of the stereomicroscope operator to be enhanced by live quantitative height measurements with depth resolutions in the micrometer range.

A new phase extraction algorithm considering high-order harmonics in fringe image processing

Keming Zhang, Jun Yao, Jubing Chen, and Hong Miao

Doc ID: 235640 Received 05 Mar 2015; Accepted 02 May 2015; Posted 04 May 2015  View: PDF

Abstract: A phase calculation method using Discrete Fourier Series (DFS) is proposed to eliminate the effects of non-sinusoidal characteristics. In this method, the fundamental coefficients are extracted from continuous Ν samples in one cycle by DFS, with which four images with π/2 interval are reconstructed, and then more accurate phase distribution can be further obtained. This method is applicable for improving the precision of the traditional four-step phase shift algorithm. Its effectiveness and accuracy are verified by both the computer simulations and moiré fringe and projecting fringe experiments with more than 80% of the phase error reduced.

Acousto-optics bandwidth broadening in a Bragg-cell based on arbitrary synthesized signal methods

Itay Peled, Zvi Kotler, and Ron Kaminsky

Doc ID: 232210 Received 17 Feb 2015; Accepted 01 May 2015; Posted 04 May 2015  View: PDF

Abstract: In this work we present the advantages of driving a multi-channel acousto-optical deflector with a digitally synthesized multi-frequency RF signal. We demonstrate a significant bandwidth broadening of ~40% by providing well-tuned phase control of the array transducers. Moreover, using a multi-frequency, complex signal we manage to suppress the harmonic deflections and return most of the spurious energy to the main beam. This method allows us to operate the AOD with more than an octave of bandwidth with negligible spurious energy going to the harmonic beams, and a total bandwidth broadening of over 70%.

Spatio-angular Minimum-variance Tomographic Controller for Multi-Object Adaptive Optics systems

Carlos Correia, Kate Jackson, Jean-Pierre Veran, David Andersen, Olivier Lardière, and Colin Bradley

Doc ID: 235008 Received 19 Feb 2015; Accepted 01 May 2015; Posted 04 May 2015  View: PDF

Abstract: Multi-object astronomical adaptive-optics (MOAO) is now a mature wide-field observation mode to enlarge the adaptive-optics-corrected field in a few specific locations over tens of arc-minutes. The work-scope provided by open-loop tomography and single conjugation is amenable to a spatio-angular Linear-Quadratic Gaussian (SA-LQG) formulation aiming to provide enhanced correction across the field with improved performance over static reconstruction methods and less stringent computational complexity scaling laws. Starting from our previous work \cite{correia14}, we use stochastic time-progression models coupled to approximate sparse measurement operators to outline a suitable SA-LQG formulation capable of delivering near optimal correction. Under the spatio-angular framework the wave-fronts are never explicitly estimated in the volume, providing considerable computational savings on 10\,m-class telescopes and beyond. We find that for Raven, a 10m-class MOAO system with two science channels, the SA-LQG improves the limiting magnitude by two stellar magnitudes when both Strehl-ratio and Ensquared-energy are used as figures of merit. The sky-coverage is therefore improved by a factor of $\sim$5.

Generalized Sine Condition

Tamer Elazhary, James Burge, Chunyu Zhao, and ping zhou

Doc ID: 235594 Received 03 Mar 2015; Accepted 01 May 2015; Posted 04 May 2015  View: PDF

Abstract: The classic Abbe sine condition relates pupil distortion to aberration with linear field dependence such as coma. This paper provides a fully generalized form of the sine condition that does not use any symmetry. It accurately predicts the change in aberration in the presence of field independent and pupil aberrations. The definitions of the image, object, and coordinate system are completely arbitrary. The relationship is verified using ray trace simulations of a number of systems that have varying degrees of complexity. The potential applications are discussed.

Single molecule localisation software applied to photon counting imaging

Klaus Suhling, Liisa Hirvonen, and Tiffany Kilfeather

Doc ID: 236296 Received 17 Mar 2015; Accepted 01 May 2015; Posted 01 May 2015  View: PDF

Abstract: Centroiding in photon counting imaging has traditionally been accomplished by a single step, noniterative algorithm, often implemented in hardware. Single molecule localisation techniques in superresolution fluorescence microscopy are conceptually similar, but use more sophisticated iterative fitting algorithms to localise the fluorophore. Here, we discuss common features and differences between single molecule localisation and photon counting imaging and investigate the suitability of single molecule localisation software for photon event localisation. We find that single molecule localisation software packages designed for super-resolution microscopy – QuickPALM, rapidSTORM and ThunderSTORM – work well when applied to photon counting imaging with a microchannel-plate-based intensified camera system: photon event recognition is excellent, fixed pattern noise is low and the microchannel plate pores can easily be resolved.

Determination of carcinogenic Fluorine in cigarettes using pulsed UV laser induced breakdown spectroscopy

Mohammed Gondal, Yusuf Habibullah, Luqman Oloore, and Mohammed Iqbal

Doc ID: 236499 Received 18 Mar 2015; Accepted 30 Apr 2015; Posted 01 May 2015  View: PDF

Abstract: A spectrometer based on pulsed UV Laser induced breakdown spectroscopy (LIBS) and high sensitive ICCD camera was developed to determine the carcinogenic substances like fluorine in various brands of cigarettes available commercially. In order to achieve the high sensitivity required for the determination of trace amounts of fluoride in cigarettes and eventually the best limit of detection, the experimental parameters (influence of incident laser energy on libs signal intensity and time response of plasma emission) were optimized. In addition, the plasma parameters like electron temperature and electron density were evaluated using Boltzman’s plot for cigarettes tobacco for the first time. To the best of our knowledge, LIBS has never been applied to determine the fluorine concentration in cigarettes. Along with the detection of flourine, other trace metals like Ba, Ca, Ni, Cu and Na were also detected in cigarettes. For determination of the concentration of flourine, calibration curve was drawn by preparing standard samples in various fluoride concentrations in tobacco matrix. The concentration of fluorine in different cigarettes tobacco samples was 234,317,341 and 360 ppm respectively, which is considered to be much higher than the safe permissible limits. The limit of detection of our LIBS spectrometer was 14 ppm for fluorine.

Dynamic tread wear measurement method for train wheels against vibrations

Guangjun Zhang, Xu Chen, Junhua Sun, and zhen liu

Doc ID: 233170 Received 28 Jan 2015; Accepted 30 Apr 2015; Posted 30 Apr 2015  View: PDF

Abstract: Dynamic tread wear measurement is difficult but significant for railway transportation safety and efficiency. Accuracies of existing methods are inclined to be affected by environmental vibrations since they are highly dependent on the accurate calibration of the relative pose between vision sensors. In this paper, we present a method to obtain full wheel profiles based on automatic registration of vision sensor data instead of traditional global calibrations. We adopt two structured light vision sensors to recover the inner and outer profiles of each wheel, and register them by the iterative closest point (ICP) algorithm. Computer simulations show that the proposed method is insensitive to noises and relative pose vibrations. Static experiments demonstrate that our method has high accuracy and great repeatability. Dynamic experiments show that the measurement accuracy of our method is 0.18mm which is an improvement about a factor two over traditional methods.

Krypton tagging velocimetry (KTV) of an underexpanded jet

Nicholaus Parziale, Eric Marineau, and Michael Smith

Doc ID: 232446 Received 25 Feb 2015; Accepted 30 Apr 2015; Posted 01 May 2015  View: PDF

Abstract: In this work, we present the excitation/emission strategy, experimental setup, and results of an implementation of krypton tagging velocimetry (KTV). KTV is performed as follows: i) seed a base flow with krypton; ii) photosynthesize metastable krypton atoms with a frequency doubled dye laser to form the tagged tracer; iii) record the translation of the tagged metastable krypton by imaging the laser induced fluorescence that is produced with an additional dye laser. The principle strength of KTV, relative to other tagging velocimetry techniques, is the use of a chemically-inert tracer. KTV results are presented for an underexpanded jet of three mixtures of varying Kr/N2 concentration. It is demonstrated that KTV can be used in gas mixtures of relatively low krypton mole fraction (0.5% Kr/99.5% N2), and the KTV data from that experiment are found to be in good agreement with an empirical fit found in the literature. We find that KTV is useful to perform instantaneous velocity measurements with metastable krypton as a chemically-inert, dilute, long-lifetime tracer in gas-phase flows.

8.2 kW high beam quality QCW face-pumped Nd:YAG slab amplifier

Chen Zhongzheng, GUO ding, Xu Ting, Baoshan Wang, Xu Jian, Xu Lin, Gao Wei, Lei Yuan, Yuan Tao, Lin Yong, Xiao Sheng, Bo Yong, Qinjun Peng, wen-qiang Lei, Da Cui, and Xu Zuyan

Doc ID: 234384 Received 10 Feb 2015; Accepted 29 Apr 2015; Posted 30 Apr 2015  View: PDF

Abstract: An eight kilowatt level quasi-continuous-wave (QCW) face-pumped 1064 nm slab laser with high beam quality was developed by a master oscillator power amplifier (MOPA) system. A single mode fiber seed laser was amplified by two-stage-single-pass Nd:YAG rod pre-amplifiers and four face-pumped Nd:YAG slab amplifiers. The slab amplifiers were well-designed with uniform pumping and uniform cooling for well-distributed thermal and stress. A dynamically feed-backed optical aberration compensation device was employed to correct low-order optical aberration, and the residue high-order optical aberration was corrected by an adaptive optics system. The QCW MOPA delivered up to an average power of 8.2 kW with pulse duration of 200 μs at repetition rate of 400 Hz. The beam quality factor was measured to be β = 3.5.

Detector-Level Spectral Characterization of the Suomi NPP VIIRS Long-Wave Infrared Bands M15 & M16

Francis Padula and Changyong Cao

Doc ID: 231313 Received 23 Dec 2014; Accepted 29 Apr 2015; Posted 29 Apr 2015  View: PDF

Abstract: The Suomi National Polar-orbiting Partnership (S-NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) Sensor Data Record (SDR) product achieved validated maturity status in March of 2014 after roughly two years of on-orbit characterization (S-NPP spacecraft launched 28 October 2011). During post-launch analysis the VIIRS Sea Surface Temperature (SST) Environmental Data Record (EDR) team observed an anomalous striping pattern in the daytime SST data. Daytime SST retrievals use the two VIIRS long-wave infrared bands: M15 (10.7 μm) and M16 (11.8 μm). To assess possible root causes due to detector-level Spectral Response Function (SRF) effects, a study was conducted to compare the radiometric response of the detector-level and operational band averaged SRFs of VIIRS bands M15 & M16. The study used simulated hyperspectral blackbody radiance data and clear-sky ocean hyperspectral radiances under different atmospheric conditions. It was concluded that the SST product is likely impacted by small differences in detector-level SRFs, and that if users require optimal system performance detector-level processing is recommended. Future work will investigate potential SDR product improvements through detector-level processing in support of the generation of Suomi NPP VIIRS climate quality SDRs.

A back-scanning step and stare imaging system with high frame rate and wide coverage

Sun Shang, dejiang wang, Dapeng Tian, and Yalin Ding

Doc ID: 234252 Received 12 Feb 2015; Accepted 29 Apr 2015; Posted 29 Apr 2015  View: PDF

Abstract: Step and stare imaging with staring arrays has become the main approach to realize wide area coverage and high resolution imagery of potential targets. In this paper, a back-scanning step and stare imaging system concept is elaborated. Compared with traditional step and stare imaging system, this system features a much higher frame rate by using a small-sized array. FSM provides backscan motion to compensate the image motion caused by continuous scanning motion of the gimbal to meet the staring requirements. Control system design is also discussed in this article, which plays an important role in this imaging system. Then a proof-of-concept back-scanning step and stare imaging system is established with a CMOS camera. Finally, slanted-edge method is used to measure the MTF of the image acquired in step and stare mode by the system. The experimental results confirm that both high frame rate and image quality improvement can be achieved by adopting this method.

Optimization of a horizontal slot waveguide biosensor to detect DNA hybridization

Charusluk Viphavakit, Michael Komodromos, Christos Themistos, Waleed Mohammed, Kyriacos Kalli, and Azizur Rahman

Doc ID: 234855 Received 18 Feb 2015; Accepted 28 Apr 2015; Posted 29 Apr 2015  View: PDF

Abstract: A full-vectorial H-field formulation-based finite element approach is used to optimize a biosensor structure incorporating a horizontal slot waveguide. It is designed to detect DNA hybridization through the change of the effective index of the waveguide structure. The key parameters, such as normalized power confinement, power density, change in effective index and sensitivity are presented by optimizing the device parameters of the slot waveguide. It is shown here that a 90.0 μm long compact Mach-Zehnder section can be designed with horizontal slot waveguide to detect DNA hybridization and for a ring resonator arrangement a sensitivity of 893.5 nm/RIU is obtained.

Detection and Monitoring of Surface Micro-Cracks by PPP-BOTDA

Farhad Ansari, Dewei Meng, and Xin Feng

Doc ID: 235293 Received 26 Feb 2015; Accepted 28 Apr 2015; Posted 29 Apr 2015  View: PDF

Abstract: Appearance of micron size surface cracks is common in structural elements such as in welded connections, beams and gusset plates in bridges. Brillouin scattering based sensors are capable of making distributed strain measurements. Pre-Pump-Pulse-BOTDA (PPP-BOTDA) provides centimeter level spatial resolution which facilitates detection and monitoring of the cracks. In the work described here, in addition to the shift in Brillouin frequency (distributed strains), change in the Brillouin Gain Spectrum (BGS) width is investigated for the detection and monitoring of surface micro-cracks. A theoretical analysis was undertaken in order to verify the rationality of the proposed method. The theoretical approach involved simulation of strain within a segment of the optical fiber traversing a crack and use of the simulated strain distribution in the opto-mechanical relations in order to numerically obtain the change in the Brillouin Gain Spectrum. The simulations revealed that the increase in crack opening displacements is associated with increase in BGS width and decrease in its peak power. Experimental results also indicated that the increases in crack opening displacements are accompanied with increases in BGS widths. However, it will be difficult to use the decrease in BGS power peak as another indicator due to practical difficulties in establishing generalized power amplitude in all the experiments. The study indicated that in combination with the shift in Brillouin frequency the increase in BGS width will provide a strong tool for detection and monitoring of surface micro-crack growths.

Measurement of roughness based on Talbot effect in reflection from rough surfaces

Masoomeh Dashtdar, Ali Mohammadzade, and S. Mohammad Ali Hosseini Saber

Doc ID: 235912 Received 10 Mar 2015; Accepted 28 Apr 2015; Posted 29 Apr 2015  View: PDF

Abstract: In the present work, the Talbot effect of a square grating is analyzed when light is reflected from a rough surface. It is shown theoretically that the scattered light intensity in the Fresnel diffraction limit depends on statistical properties of the rough surface, the angle of incidence of the light, the grating period, and a geometric coefficient, related to the ratio of distance of the rough surface and the observation plane from the grating. At Talbot distances of the grating, the surface height difference function, in terms of multiplication of the Talbot number, the grating period, and the geometric coefficient is the modulation transfer function (MTF) of the scattering in reflection from the rough surface. If the argument of the height difference function is larger than twice the surface correlation length, the height difference function is constant for different spatial frequencies. Therefore, the square wave is reproduced with smaller contrast. The surface roughness can be obtained by measuring the contrast at different incident angles. It is also shown that the contrast measurements in both reflection and transmission, provide the refractive index of transparent samples with a rough surface. In experimental studies the roughness of three metal standard rough surfaces are determined in different angles of incidence. Also, the refractive index of a sheet glass with a rough surface is obtained. The results are quite consistent.

Photoelastic properties of NaBi(MoO4)2 crystals

Rostyslav Vlokh, Oleh Krupych, Marian Kushnirevych, and Oksana Mys

Doc ID: 236199 Received 13 Mar 2015; Accepted 28 Apr 2015; Posted 29 Apr 2015  View: PDF

Abstract: In this work we present the results of comprehensive studies of the piezooptic and elastooptic effects in NaBi(MoO4)2 crystals. The full matrices of the piezooptic and elastooptic coefficients for the NaBi(MoO4)2 crystals are obtained for the first time. The acoustooptic effect in the sodium-bismuth double molibdate is analyzed for the case of interactions of optical waves with the slowest acoustic waves. It is shown that the crystals under analysis can be efficiently used as working elements for the collinear acoustooptic tunable filters.

Description of particle induced damage on protected silver coatings

Stefan Schwinde, Mark Schuermann, Paul-Johannes Jobst, Norbert Kaiser, and Andreas Tünnermann

Doc ID: 236643 Received 24 Mar 2015; Accepted 28 Apr 2015; Posted 28 Apr 2015  View: PDF

Abstract: In the visible to infrared spectral range, highly-reflective silver mirrors are applied in the manufacture of optical instruments such as telescopes. However, it is still difficult to combine high reflectivity and long-term stability of the protected silver coating. We show that the deposition of impervious protective layers is necessary but often not sufficient for long-term environmental stability. Hygroscopic air borne particles absorbed by the protections surface attract water molecules and form a solution. This solution first damages the protection, subsequently permeates the protection and finally damages the silver whereby the reflectivity is reduced. We demonstrate this particular damage mechanism with different experiments and describe this mechanism in detail.

Supercontinuum generation in strip/slot hybrid waveguide with flat and low dispersion

Yuchao Zhang, Hongjun Liu, Qibing Sun, Nan Huang, and Zhaolu Wang

Doc ID: 233471 Received 29 Jan 2015; Accepted 27 Apr 2015; Posted 27 Apr 2015  View: PDF

Abstract: A strip/slot hybrid waveguide with double horizontal silicon nanocrystals (Si-nc) slots is proposed to achieve flat and low dispersion with four zero dispersion wavelengths (ZDWs). By tuning structural parameters of the waveguide, dispersion tailoring is characterized fully. The flat dispersion varying between -13 and 14 ps/(nmkm) is obtained over a 845 nm bandwidth. A broadband supercontinuum spectrum, spanning from 1.15 μm to 3.65 μm in -15 dB level, was generated in this waveguide pumped by femotsecond pulse at 1.86 μm. The results indicate that the waveguide has a great potential in both near-infrared and mid-infrared nonlinear applications.

Single-shot wavefront stability of High-Harmonic Generation

Swen Künzel, Gareth Williams, Willem Boutu, Eric Galtier, Benjamin Barbrel, Hae Ja Lee, Bob Nagler, Ulf Zastrau, Guillaume Dovillaire, Hamed Merdji, Philippe Zeitoun, Marta Fajardo, and Richard Lee

Doc ID: 234963 Received 25 Feb 2015; Accepted 27 Apr 2015; Posted 27 Apr 2015  View: PDF

Abstract: We report on the single-shot stability of intensity and spatial phase of high-harmonic generation (HHG). The intensity stability is measured for each high-harmonic (HH) order with a spectrometer. Additionally the spatial phase is measured with an XUV wavefront sensor for a single HH order measured in a single shot, which according to our knowledge was not reported before with a Hartmann wavefront sensor. Furthermore we compare the single-shot measurement of the spatial phase with time-integrated measurements and we show that the XUV wavefront sensor is a useful tool to simultaneously optimize the spatial phase and intensity of high-harmonic generation within the available HHG parameter range used in this study.

Camera calibration by multiplexed phase encoding of coordinate information

Rigoberto Juarez-Salazar, Wuiyevaldo Guerrero-Sanchez, Carlos Robledo-Sanchez, and Jorge González-García

Doc ID: 233247 Received 26 Jan 2015; Accepted 27 Apr 2015; Posted 28 Apr 2015  View: PDF

Abstract: A simple camera calibration method based on the principle of phase-encoding and coordinate transformation is proposed. We use a reference coordinate frame encoded as a phase distribution by multiplexing the $x$- and $y$- directions. From this, we suggest a phase demodulation system. The coordinate transformation induced by the imaging is exploited to estimate the camera parameters by using the least-squares method. Thus, a robust and non-iterative estimation scheme is obtained. Simulations and experimental results show the feasibility of the proposal. Because of the potential for calibrating projectors, the proposed method could be used to calibrate fringe-projection systems.

Finite Sampling Corrected 3D Noise with Confidence Intervals

David Haefner and Stephen Burks

Doc ID: 234553 Received 12 Feb 2015; Accepted 27 Apr 2015; Posted 28 Apr 2015  View: PDF

Abstract: In the 90's, NVESD engineers developed an approximation to the noise 3D power spectral density for imaging systems known as 3D noise. To characterize a sensor in terms of its 3D noise values, a finite number of samples in each of the 3 dimensions (2 spatial, 1 temporal) are performed. In this correspondence, we develop the full sampling corrected 3D noise measurement and the corresponding confidence bounds. The accuracy of these methods is demonstrated through Monte Carlo Simulations. Both the sampling correction as well as the confidence intervals can be applied a posteriori to the classic 3D noise calculation. The Matlab functions associated with work can be found on the Mathworks file exchange.

A high-performance reconfigurable coincidence counting unit based on an FPGA

Byung Kwon Park, Yong-Su Kim, Osung Kwon, Sang-Wook Han, and Sung Moon

Doc ID: 236110 Received 23 Mar 2015; Accepted 26 Apr 2015; Posted 27 Apr 2015  View: PDF

Abstract: We present a high-performance reconfigurable coincidence counting unit (CCU) using a low-end field programmable gate array (FPGA) and peripheral circuits. Because of the flexibility guaranteed by the FPGA program, we can easily change system parameters, such as internal input delays, coincidence configurations, and coincidence time window. In spite of a low-cost implementation, the proposed CCU architecture outperforms previous ones in many aspects: it has 8 logic inputs and 4 coincidence outputs that can measure up to 8-fold coincidences. The minimum coincidence time window and the maximum input frequency are 0.47 ns, and 163 MHz, respectively. The CCU will be useful in various experimental research areas, including the field of quantum optics and quantum information.

Iterative phase retrieval algorithms: Part I. Optimization

John Sheridan, Changliang Guo, and Shi Liu

Doc ID: 232602 Received 19 Jan 2015; Accepted 26 Apr 2015; Posted 27 Apr 2015  View: PDF

Abstract: Two modified Gerchberg Saxton (GS) iterative phase retrieval algorithms are proposed. The first we refer to as the Spatial Phase Perturbation GS algorithm (SPP GSA). The second is a combined GS Hybrid Input Output algorithm (GS/HIOA). In this paper (Part I), it is demonstrated that the SPP GS and GS/HIO algorithms are both much better at avoiding stagnation during phase retrieval, allowing them to successful locate superior solutions compared to either the GS or the HIO algorithms. The performances of the SPP GS and GS/HIO algorithms are also compared. Then the Error Reduction (ER) algorithm is combined with the HIO algorithm (ER/HIOA) to retrieve the input object image and the phase given only some knowledge of its extent and the amplitude in the Fourier domain. In Part II, the algorithms developed here are applied to carry out Known Plaintext and Ciphertext Attacks (KPCAs) on both Amplitude Encoding (AE) and Phase Encoding (PE) Double Random Phase Encryption (DRPE) systems. Significantly, ER/HIOA is then used to carry out a Ciphertext-Only Attack (COA) on AE DRPE systems.

Ambient condition desensitization of a fiber Raman temperature sensing system based on a dynamic sampling-correction scheme

Tianying Chang, Miao Yu, Ye Liu, and Hong-Liang Cui

Doc ID: 232657 Received 28 Jan 2015; Accepted 24 Apr 2015; Posted 27 Apr 2015  View: PDF

Abstract: One of the most important performance indicators of a fiber optic distributed temperature sensing (DTS) system is its operational stability, which depends on the performance of each device making up the system. Such individual device performance itself is affected by temperature and other environmental conditions. As a result, ambient fluctuations invariably lead to measurement uncertainties and drifts, seriously degrading the system performance. To ameliorate such adverse effects of the environment, we propose a dynamic sampling-correction scheme, which we have implemented on our fiber optic Raman DTS system, resulting in an average temperature error within 1℃ when the main chassis undergoes a temperature variation over the range -25 ~ 45 ℃. The drastically improved system stability foreshadows better performance and reliability in engineering applications.

SLM-based laboratory simulations of Kolmogorov and non-Kolmogorov anisotropic turbulence

Italo Toselli, Olga Korotkova, Xifeng Xiao, and David Voelz

Doc ID: 234229 Received 09 Feb 2015; Accepted 24 Apr 2015; Posted 24 Apr 2015  View: PDF

Abstract: In this paper we present a laboratory set-up to simulate anisotropic, non-Kolmogorov turbulence. A sequence of numerical phase screens that incorporate the turbulence characteristics were applied to a spatial light modulator (SLM) placed in the path of a laser beam with a Gaussian intensity profile and the resulting far-field intensity patterns were recorded by a CCD camera. The values of scintillation at the position of the maximum intensity were extracted from the images and compared with theoretical values. Our experimental results show a trend that is in agreement with known theoretical expressions, however the turbulence rescaling due to anisotropy shows some discrepancy with theory and requires more investigation.

Surface characteristics modeling and performance evaluation of urban building materials using LiDAR data

Yu Liang and Xiaolu Li

Doc ID: 236759 Received 23 Mar 2015; Accepted 24 Apr 2015; Posted 24 Apr 2015  View: PDF

Abstract: The analysis of light detection and ranging (LiDAR) intensity data to extract surface features is of great interest in remote sensing research. One potential application of LiDAR intensity data is target classification. A new bidirectional reflectance distribution function (BRDF) model is derived for targets characterization of both rough surface and smooth surface. Based on the geometry of our coaxial full-waveform LiDAR system, the integration method is improved through coordinate transformation to establish the relationship between the BRDF model and intensity data of LiDAR. A series of experiments using typical urban building materials are implemented to validate the proposed BRDF model and integration method. The fitting results show that three parameters extracted from the proposed BRDF model can distinguish the urban building materials from perspectives of roughness, specular reflectance, and diffuse reflectance. A comprehensive analysis of these parameters will help charactering surface feature in a physically rigorous manner. © 2015 Optical Society of America.

“Albedo dome”: A method for measuring spectral flux-reflectance in a laboratory

Bonnie Light, Regina Carns, and Stephen Warren

Doc ID: 232083 Received 07 Jan 2015; Accepted 24 Apr 2015; Posted 04 May 2015  View: PDF

Abstract: A method for accurate measurement of spectral flux-reflectance (albedo) in a laboratory is presented. The approach uses an acrylic hemispheric dome, which, when placed over the surface being studied, serves two functions: (i) it creates an overcast “sky” to illuminate the target surface from all directions within a hemisphere, and (ii) serves as a platform for measuring incident and backscattered spectral radiances, which can be integrated to obtain fluxes. The fluxes are relative measurements and because their ratio is used to determine flux-reflectance, no absolute radiometric calibrations are required. The dome and surface must meet minimum size requirements based on the scattering properties of the surface. Comparison between field and laboratory albedo of a portable test surface demonstrates the viability of this method.

THz wave transmission within the metal-clad antiresonant reflecting hollow waveguides

Jiamin Liu, Huawei Liang, Min Zhang, and Hong Su

Doc ID: 233035 Received 22 Jan 2015; Accepted 23 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: We present the transmission characteristics of THz waves in the metal-clad antiresonant reflecting hollow waveguides. The effects of the waveguide structure on the blueshift of the resonance frequency are studied comprehensively. In particular, we find that the blueshift of the resonance frequency is strongly affected by the interval between two dielectric slabs. By changing the interval, we obtain that the maximum frequency-tuning-range is up to 2030 GHz, and the maximum sensitivity of the resonance frequency shift is up to 6950 GHz/mm at the resonance order of m = 1. When the THz wave is far away from the resonance frequency, both the loss and the dispersion of the guide modes are very low.

Tunable multiwavelength Tm-doped fiber laser based on multimode interference effect

Tianshu Wang, Peng Zhang, Wanzhuo Ma, Keyan Dong, and Huilin Jiang

Doc ID: 233398 Received 28 Jan 2015; Accepted 23 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: A simple multiwavelength Tm-doped fiber laser at 2μm band based on multimode interference (MMI) is proposed and experimentally demonstrated. In this scheme, a 4m Tm-doped singlemode fiber is pumped by a 1568nm laser, and a singlemode-multimode-singlemode (SMS) fiber structure is used as an MMI filter in which the multimode fiber is used to tune the laser. Laser operation of up to three wavelengths is obtained based on the MMI filter. The wavelengths can be tuned by adjusting the polarization controller (PC) and rotating the multimode fiber in the SMS structure, and the tuning region is about 24nm, i.e., 1892-1916nm. The side-mode suppression ratio (SMSR) of the laser is about 54dB. The 3dB linewidth is less than 0.04nm. Peak fluctuation at each wavelength is analyzed, and the results show that the power fluctuation is less than 3dB around the average power.

Radiometric calibration method for large aperture infrared system with high dynamic range

Zhiyuan Sun, Songtao Chang, and wei zhu

Doc ID: 233549 Received 30 Jan 2015; Accepted 23 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: Infrared radiometric measurement could afford important data for missile defense system. When observation is carried out by ground-based infrared systems, missile is characterized by long distance, small size and large variation of radiance. Therefore, the infrared systems should be manufactured with larger aperture to enhance detection ability and calibrated at broader dynamic range to extend measurable radiance. Nevertheless, the frequently-used calibration methods demand extended area blackbody with broad dynamic range or a huge collimator for filling system’s field stop, which would increase the manufacturing costs and difficulties greatly. To overcome this restriction, a calibration method based on amendment of inner and outer calibration is proposed. Firstly, the principles and procedures of this method are introduced. Then a shifting strategy of infrared system for measuring targets with large fluctuations of infrared radiance is put forward. Finally, several experiments are performed on a shortwave infrared system with Φ400mm aperture. The results indicate that the proposed method can not only ensure the accuracy of calibration but have the advantage of low cost, low power and high motility. Hence it is an effective radiometric calibration method in outfield.

Planar spoof plasmonic ultra-wideband filter based on low-loss and compact terahertz waveguide corrugated with dumb-bell grooves

Yong Jin Zhou and Bao Jia Yang

Doc ID: 234721 Received 17 Feb 2015; Accepted 22 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: Although subwavelength planar terahertz (THz) plasmonic devices can be implemented based on planar spoof surface plasmons (SPs), they still suffer from a little high propagation loss. Here the dispersion and propagation characteristics of the spoof plasmonic waveguide composed of double metal strips corrugated with dumb-bell grooves have been investigated. It’s been found that much lower propagation loss and longer propagation length can be achieved based on the waveguide, comparing with the conventional spoof plasmonic waveguide with rectangle grooves. Moreover, the waveguide can implement a decrease in size about 22%. An ultra-wideband THz plasmonic filter for planar circuits has been demonstrated based on the proposed waveguide. The experimental verification at the microwave frequency has been conducted by scaling up the geometry size of the filter.

Polarization holography for vortex retarders recording : laboratory demonstration

Pierre Piron, Pascal Blain, Marc Décultot, Dimitri Mawet, and Serge Habraken

Doc ID: 235018 Received 20 Feb 2015; Accepted 22 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: This paper will present a prototype of the first set of vortex retarders made of liquid crystal polymers recorded by a polarization holography. Vortex retarders are birefringent plates characterized by a rotation of their fast axis. The liquid crystal possesses birefringent properties and they are locally orientable. Their orientation is defined by the local orientation of the recording field. Polarization holography is a purely optical recording method. It is based on the superimposition of coherent and differently polarized beams. It is used to shape the electric field pattern to enable the recording of vortex retarders. The paper details the mathematical model of the superimposition process. The recording setup is exposed, it is characterized by a nearly common path interferometer. Two sets of measurements allowing the prediction of the retarder’s features are presented and compared. Finally, the experimen- tally recorded retarder is shown, its characteristics are investigated and compared to the predicted ones.

Dispersion and anisotropy of thermo-optic coefficients in tetragonal GdVO4 and YVO4 laser host crystals: Errata

Konstantin Yumashev, Pavel Loiko, Nikolai Kuleshov, and Vladimir Matrosov

Doc ID: 236036 Received 11 Mar 2015; Accepted 22 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: We addressed errors found in our measurements of thermo-optic coefficients and thermal coefficients of the optical path (TCOP) in tetragonal vanadates, YVO4 and GdVO4 [Appl. Opt. 52, 698 (2013)]. Modified thermo-optic dispersion formulas are presented for these laser host crystals.

Evanescent-field-coupled guided-mode sensor based on waveguide grating

Dmitry Nesterenko, Zouheir Sekkat, and Shinj Hayashi

Doc ID: 226836 Received 13 Nov 2014; Accepted 22 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: A guided-mode sensor with a dielectric waveguide grating formed on a thin reflective film using a Kretschmann configuration is proposed. Numerical results based on a finite element method approach indicate a significant resolution improvement due to the excitation of a guided mode supported by the waveguide grating – sensing media system. The applicability of waveguide theory to the design of waveguide gratings is validated by a comparison to the exact electromagnetic theory. Strong localization of an electromagnetic field in the sensing media within the grating with intensity enhancement up to two orders of magnitude is demonstrated. The sensor has a potential for biological sensing and imaging applications.

Detection and characterization of optical vortex by branch point potential method: analytical and simulation results

abolhasan mobashery, Morteza Hajimahmoodzadeh, and Hamid Fallah

Doc ID: 228973 Received 03 Dec 2014; Accepted 22 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: Singularities are discontinuity in optical wavefront that create when optical wave are propagated in strongly turbulent atmosphere. Presence of singularities in wavefront severely degraded the Adaptive optics correction performance, so detection of them is so important. Gradient of wavefront phase that is measured by the Shack Hartmann wavefront sensor, in the presence of singularities, can be considered as a rotational and a rotational part. Rotational part of phase gradient that originate from the phase singularities, can be considered as a vector potential based on Helmholtz-Hodge decomposition. In this article we investigate detection of phase singularities based on a vector potential that named as a branch point potential method. We presented here analytical and simulation results of detection general from of singularities and their characterization. Our simulations show that the importance of singularities detection.

Fast and robust automatic calibration for single-shot dual-wavelength digital holography based on speckle displacements

davood khodadad, Per Bergström, Emil Hallstig, and Mikael Sjodahl

Doc ID: 231191 Received 22 Dec 2014; Accepted 22 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: The objective of this paper is to describe a fast and robust automatic single-shot dual-wavelength holographic calibration method that can be used for online shape measurement applications. We present a model of the correction in two terms for each lobe, one to compensate the systematic errors caused by off-axis angles and the other one for the curvature of the reference waves, respectively. Each hologram is calibrated independently without a need for an iterative procedure or information of the experimental set-up. The calibration parameters are extracted directly from speckle displacements between different reconstruction planes. The parameters can be defined as any fraction of a pixel to avoid the effect of quantization. Using the speckle displacements, problems associated with phase wrapping is avoided. The procedure is shown to give a shape accuracy of 34 μm using a synthetic wavelength of 1.1 mm for a measurement on a cylindrical test object with a trace over a field of view of 18 mm × 18 mm.

Three-dimensional combined pyrometric sizing and velocimetry of combusting coal particles II. Pyrometry

Pal Toth, Teri Snow, Arpad Palotas, Tery Ring, and Eric Eddings

Doc ID: 232693 Received 21 Jan 2015; Accepted 22 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: Knowledge of the in situ temperature, size, velocity, and number density of a population of burning coal particles yields insight into the chemical and aerodynamic behavior of a pulverized coal flame (e.g., through means of combustion model validation). Sophisticated and reasonably accurate methods are available for the simultaneous measurement of particle velocity and temperature; however, these methods typically produce single particle measurements in small analyzed volumes and require extensive instrumentation. We present a simple and inexpensive method for the simultaneous, in situ, three-dimensional (3D) measurement of particle velocity, number density, size, and temperature. The proposed method utilizes a combination of stereo imaging, 3D reconstruction, multicolor pyrometry and digital image processing techniques. The details of theoretical and algorithmic backgrounds are presented, along with examples and validation experiments. By utilizing numerical simulations, rigorous uncertainty quantification is performed in order to estimate the accuracy of the method and explore how different parameters affect measurement uncertainty. The method is described in two parts. The second part, presented in this paper, describes particle temperature and size measurement in overexposed emission images.

Ciphertext-only attack on the JTC-based cryptosystem with sizes and locations of the plaintext and the key code unknown

jianjun cai, xue shen, Chao Lin, and Huilong Wu

Doc ID: 233480 Received 29 Jan 2015; Accepted 21 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: We demonstrate an effective ciphertext-only attack (COA) method on joint transform correlator-based cryptosystem with sizes and locations of the plaintext and the key code unknown. In our method, we first obtain the signal domain support by using the method, which is based on the geometry of the autocorrelation support of the object. And then, the hybrid input-output (HIO) algorithm is used to retrieve the plaintext. Compared with the work on COA recently reported by Zhang et al., our proposed method needs less resources and much less iteration times for binary image to retrieve the plaintext. Simulation results are provided to demonstrate the validity of the presented method.

Experimental Research on the MRC Diversity Reception Algorithm for UV Communication

Li Guo, Xidong Mu, Dedan Meng, Kunlun Liu, Dahai Han, and Weilun Feng

Doc ID: 235550 Received 03 Mar 2015; Accepted 21 Apr 2015; Posted 29 Apr 2015  View: PDF

Abstract: Ultraviolet(UV) communication is an emerging communication method with non-line-of-sight (NLOS), anti-interference, and anti-interception capabilities, along with a high flexibility and reliability. Herein, the maximum ratio combining (MRC) diversity reception algorithm for the UV communication system is studied. Simulation and experimental results indicate that single input and multiple output (SIMO) is useful and achievable, with an obvious diversity gain, and the MRC diversity reception algorithm can reduce the system bit error rate (BER) more effectively than the equal-gain combining (EGC) method. The simulation and experimental results are analyzed and the differences between them are discussed. These results provide guidelines for UV communication system design and implementation.

Compensation of drift by using multichannel integrated Young interferometer

Sanna Aikio, Marianne Hiltunen, and Jussi Hiltunen

Doc ID: 231085 Received 18 Dec 2014; Accepted 21 Apr 2015; Posted 21 Apr 2015  View: PDF

Abstract: Polymer based integrated Young interferometer sensor chips have proven to be sensitive, and have potential to be mass-manufacturable. The sensing method is however disturbed by the mechanical drifts, thus requiring well stabilized and isolated measurement setups that limit its applicability to low cost readers for rapid diagnostics. In this paper, we derive an analytical method for the compensation of mechanical drift by using a multichannel integrated Young interferometer chip having two reference channels. The compensation method was demonstrated by quantitative measurements with a three-channel integrated polymeric Young interferometer sensor chip. By applying the compensation method, the mechanical drift was reduced up to 84%, and the repeatability of the signal quantification was improved by reducing the standard deviation of the sensor responses up to 43%.

Burst shaping in a fiber-amplifier-chain seeded by a gain-switched laser diode

Rok Petkovsek, Jaka Petelin, and Bostjan Podobnik

Doc ID: 235775 Received 06 Mar 2015; Accepted 21 Apr 2015; Posted 21 Apr 2015  View: PDF

Abstract: A low-power source, such as a gain-switched laser diode usually requires several amplification stages to reach sufficient power levels. When operating in burst mode, a correct input burst shape must be determined in order to compensate for gain saturation of all amplifier stages. In this paper we report on closed-form equations that enable saturation compensation in multi-amplifier setups, which eliminates the need for an adaptive feedback loop. The theoretical model is then evaluated in an experimental setup.

Experimental Demonstration of Polarization Division Multiplexing of Chaotic Laser Secure Communications

Xinyu Dou, Hongxi Yin, Hehe Yue, and Yu Jin

Doc ID: 234435 Received 11 Feb 2015; Accepted 20 Apr 2015; Posted 21 Apr 2015  View: PDF

Abstract: Optical polarization-division-multiplexing (PDM) can double the capacity of the communication system. In this paper, PDMs between a conventional fiber-optic channel and a chaos encrypted channel, and between two chaos encrypted channels are proposed and experimentally investigated. The bit rate for each channel is 1.25 Gb/s, while the transmission in the standard single-mode fiber (SSMF) can be up to 22.54 km. The effect of the mutual power leakages on the receiver quality is experimentally explored, which are induced by the variation of polarization direction during the propagating process. In addition, the effect of optical launched power at the transmitter side on the Q-factor is tested and analyzed.

Coherent Exciton Mechanism of 3D Quantum Optical Lithography

Eugen Pavel

Doc ID: 234763 Received 17 Feb 2015; Accepted 20 Apr 2015; Posted 21 Apr 2015  View: PDF

Abstract: 2D and 3D effects observed in Quantum Optical Lithography indicate the existence of a long-distance energy migration, greater than 500 nm, to a reaction center with a diameter smaller than 1 nm. Confinement effect was obtained by energy transfer of coherent Frenkel excitons in an electric field gradient followed by a cooperative process of rare-earth ions in a fluorescent photosensitive glass-ceramics. A mechanism is proposed and discussed in order to explain the breakthrough of the diffraction limit of light. Fluorescent photosensitive glass-ceramics act as a coherent perfect absorber, a time –reversed laser.

Dual-wavelength filters based on two-dimensional photonic crystal degenerate modes with a ring dielectric rod inside defect cavity

Huizhen Xu, Zhong Ronghua, Xiulin Wang, and Huang Xin

Doc ID: 235046 Received 20 Feb 2015; Accepted 20 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: A tunable dual-wavelength filter based on degenerate modes with a ring dielectric rod inside the single point defect cavity is proposed. The band structures and mode profiles are computed by the plane-wave expansion (PWE) method. The normalized transmission spectra for this structure are investigated by using the two-dimensional finite-difference time-domain (FDTD) method. The two orthogonal output modes of the filter can be regarded as the combination of the original degenerate cavity modes and both excited due to the introduced perturbation rod. The influences of the perturbation rod on the localized modes, band separations and the tuning ranges are all investigated. With the ring dielectric rod being introduced into the defect, a wider wavelength tuning range can be obtained, which is superior to that of the filter based on cavity with a larger radius rod. The proposed filter has a simple structure and may be potentially applied in various integrated circuits, such as dual-wavelength filtering or multi-channel drop filters.

kW-level narrow linewidth fiber amplifier seeded by a fiber Bragg grating based oscillator

Jinping Hao, Hong Zhao, Dayong Zhang, Liming Zhang, and Kun Zhang

Doc ID: 212809 Received 03 Mar 2015; Accepted 20 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: An all-fiber narrow linewidth amplifier with a seed based on narrow linewidth FBGs is demonstrated. The fiber amplifier achieves a narrow bandwidth output of 823 W, with the opto-optic efficiency of 84.5%. The pair of FBGs in the seed configuration helps to assure a narrow linewidth of the laser as 0.08 nm. In the laser profile, a cladding stripper with a sectional structure is introduced, which realizes high pump power leakage with high efficiency. Besides, the impact of seed linewidth and fiber length on the SBS threshold in a narrow bandwidth laser is studied and discussed. Based on the analysis, ways to inhibit SBS onset and scale power output are found and suggested.

Influence of substrate temperatures on the properties of GdF3 thin films with quarter wave thickness in the ultra violet region

Jingcheng Jin, Chunshui Jin, Chun Li, Wenyuan Deng, and Shun Yao

Doc ID: 232725 Received 21 Jan 2015; Accepted 20 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: High quality coatings of fluoride materials are extraordinary demanded in deep ultraviolet (DUV) lithography. Gadolinium fluoride (GdF3) thin films were prepared by thermal boat evaporation process at different substrate temperatures. GdF3 thin film was set as quarter wave thickness (∼27nm) with regard to their common use in DUV/VUV optical stacks, these thin films may significantly differ in nanostructural properties at corresponding depositing temperatures which would crucially influence the performance of the multilayers. The measurement and analysis of optical, structural and mechanical properties of GdF3 thin films have been performed in a comprehensive characterization cycle. It was found that depositing GdF3 thin films at relative higher temperature would form a rather dense, smooth, homogeneous structure within this film thickness scale.

Numerical investigation of side emission from large-area vertical-cavity surface lasers.

Kousuke Torii, Masahiro Miyamoto, Hideyuki Naito, Yuta Aoki, Akira Higuchi, Takehiro Nagakura, Nobuto Kageyama, Hiroki Aoshima, Takenori Morita, Junya Maeda, and Harumasa Yoshida

Doc ID: 233168 Received 26 Jan 2015; Accepted 20 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: For large-area ion-implanted vertical-cavity surface-emitting lasers (VCSELs), side emission from edges of a chip disturbs laser emission of a VCSEL mode, and suppression of it is fundamental. In this paper, we present results of numerically investigation of the side emission from large area VCSELs. We have modeled a VCSEL structure by an infinitely broaden layer structure with mirror loss of edge surfaces. Estimated threshold gains indicate that laser emission occurs either in a VCSEL mode or an edge emitting Fabri-Perrot (EEFP) mode. Calculated emitter length dependence of the threshold gain of these modes shows good agreement with experimental results, and the side emission is verified to be the laser emission of the EEFP mode. We have also discussed the way to suppress the side emission, and confirmed that our recent achievement of over 200 W quasi-continuous-wave output from an ion-implanted VCSEL array is owing to both anti reflection coatings of the edges and introduction of optical losses in ex-emitter regions.

Advanced method of phase shift measurement from variances of interferograms differences

Vladimir Minaev, Gennady Vishnyakov, Gennady Levin, and Nikolay Nekrasov

Doc ID: 233491 Received 03 Feb 2015; Accepted 20 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: A new approach to the problem of measuring the phase shift from variances of interferograms differences based on Fourier-domain analysis is proposed. It is shown that the use of true variance of the interferograms differences and spatial apodization of interferograms increases the accuracy of the phase shift the measurement. Numerical simulations and experiments are presented.

Infrared hollow optical-fiber probes for reflectance spectral imaging Infrared hollow optical-fiber probes for reflectance spectral imaging

Yuji Matsuura, Chenhui Huang, and Saiko Kino

Doc ID: 233552 Received 03 Feb 2015; Accepted 20 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: Systems for infrared reflectance imaging are built with an FT-IR spectrometer, hollow -optical fibers, and a high-speed infrared camera. To obtain reflectance images of biological samples, an optical-fiber probe equipped with a light source at the distal end and a hybrid fiber probe composed of fibers for beam radiation and ones for image detection are developed. By using these systems, reflectance spectral images of a thin film of fat on a tooth that provides reflectance of around 4% are successfully acquired.

Nonlinear optical response of cavity optomechanical system with second-order coupling

Ka-Di Zhu, Chong Wang, and huajun chen

Doc ID: 233724 Received 05 Feb 2015; Accepted 20 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: We theoretically investigate the optical response of a cavity optomechanical system via the nonlinear coupling between the optical and mechanical resonators, which is expected to be strong. Our result shows that the nonlinear coupling has a significant influence on the optical bistability. We compare the transmission spectrum of nonlinear coupling approximated to second order with that of linear coupling, and observe a shift between the emission peak, which demonstrates the energy level modification caused by the nonlinear coupling. With this nonlinear optomechanical phenomenon, a theoretical method is proposed to obtain the mechanical frequency and the second-order coupling constant. This method can eliminate the influence caused by the first order coupling, which enables the detection of second-order coupling constant much easier

High Axial-Resolution Full-Field Optical Coherence Microscopy Using Tungsten Halogen Lamp and Liquid-Crystal-Based Achromatic Phase Shifter

Sheng-Hua LU, Wei-Chang Liu, and Jung-Ping Liu

Doc ID: 234696 Received 17 Feb 2015; Accepted 20 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: A high axial-resolution full-field optical coherence microscope (FFOCM) for topography and tomography applications is presented. The FFOCM is based on a polarization Linnik interference microscope equipped with a tungsten halogen lamp. The phase difference between the reference and test beams in the microscope is precisely and quickly shifted by using an achromatic liquid-crystal phase shifter (LCPS). The cross-sectional amplitude and phase maps of an interferogram are retrieved by using three-step phase-shifting technique. The LCPS consists of three identical nematic liquid-crystal (NLC) cells sandwiched between two quarter-wave plates so that it functions as a typical QHQ (quarter-half-quarter) phase shifter. Instead of using high-cost NLC cells with precise thickness of half-wave retardation, a new method is proposed to operate thicker NLC cells without scarifying the axial resolution. Experimental results reveal that the FFOCM is able to perform three-dimensional micrometerresolution imaging.

Chromatic confocal matrix sensor with actuated pinhole arrays

Matthias Hillenbrand, Robert Weiß, Csaba Endrödy, Adrian Grewe, Stefan Sinzinger, and Martin Hoffmann

Doc ID: 233114 Received 26 Jan 2015; Accepted 20 Apr 2015; Posted 24 Apr 2015  View: PDF

Abstract: We present two versions of a chromatic confocal matrix sensor for the snapshot acquisition of three-dimensional objects. The first version contains separate illumination and detection pinhole arrays while the second version uses a single pinhole array in double pass. The discrete lateral measurement points defined by the illumination and detection pinhole arrays are evaluated in parallel with a hyperspectral detection system. As this approach enables the spectrometric evaluation of all lateral channels multi-layer objects can be analyzed. To increase the lateral resolution the pinhole arrays are moved through micro-mechanical actuators. The paper includes a quantitative evaluation of the chromatic-confocal subsystem and proof-of-principle experiments with the full sensor system.

Thermally induced phase mismatching in a repetitively Gaussian pulsed pumping KTP crystal: a spatio-temporal treatment

Mohammad Sabaeian, Mostafa Mohammad Rezaee, Alireza Motazedian, Fatemeh Sedaghat Jaliladbadi, Iman Khazrak, and Hadi Askari

Doc ID: 237571 Received 06 Apr 2015; Accepted 19 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: Thermally induced phase mismatching (TIPM) has been proven to be an influential issue in nonlinear phenomena. It occurs when refractive indices of crystal are changed due to temperature rise. In this work, the authors report on a modeling of spatio-temporal dependence of TIPM in a repetitively pulsed pumping KTP crystal. Gaussian profiles for both spatial and temporal dependences of pump beam were used to generate second-harmonic waves (SHWs) in a type II configuration. This modeling is of importance in predicting the nonlinear conversion efficiency of crystals when heat is loaded in the system. To this end, at first, an approach to solve the heat equation in a repetitively pulsed pumping system with considering the temperature dependence of thermal conductivity and realistic cooling mechanisms such as conduction, convection, and radiation is presented. The TIPM is then calculated through the use of experimental thermal dispersion relations of KTP crystal. The results show how accumulative behaviors of temperature and TIPM (with its reverse sign) happen when the number of pulses is increased. Fluctuations accompanying temperature and TIPM were observed which were attributed to the off-time between successive pulses. Moreover, in this work, a numerical procedure for solving a repetitively pulsed pumped crystal is introduced. This procedure enables us to solve the problem with home-used computing machines.

Numerical simulations of the ultra-broadband supercontinuum generation by dual-wavelength pumping in photonic crystal fiber with two zero dispersion wavelengths

Meisong Liao, Xia Li, Juanjuan Gao, Lei Zhang, and wanjun bi

Doc ID: 233844 Received 04 Feb 2015; Accepted 19 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: Ultra-broadband supercontinuum has received considerable attention due to its numerous applications in practice. An ultra-broadband supercontinuum spanning from 426 nm to 2954 nm is generated numerically in this paper. It is achieved by dual-wavelength pumping with a specially designed silica photonic crystal fiber which has two widely separated zero dispersion wavelengths. Additionally, the wavelengths of dual-wavelength pumping are both located in the anomalous dispersion regime in our investigation, which differs from researches ever reported. Detailed physical mechanisms as well as interaction between the injected two pulses are discussed explicitly. With the introduction of a second pump pulse in infrared region, blue shifted dispersive wave is excited, turning out to be advantageous to extend supercontinuum further into ultraviolet. Interestingly, the infrared edges remain unchanged whether a pulse in near infrared is added or not. The pulse synchronization issue is studied thoroughly and the conclusion that the two pulses can encounter within the used fiber length is declared.

Use of High Dynamic Range (HDR) Imaging for Quantitative Combustion Diagnostics

Davide Giassi, Marshall Long, and Bolun Liu

Doc ID: 235837 Received 09 Mar 2015; Accepted 19 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: High dynamic range (HDR) imaging is applied to quantitative combustion diagnostics in coflow laminar diffusion flames as a way to improve signal-to-noise ratio (SNR) and measurement sensitivity. The technique relies on the combination of partially saturated frames into a single unsaturated image and in this work the effectiveness of the HDR approach is demonstrated when applied to two-color ratio pyrometry. Specifically it is shown than an increase in SNR results in more precise temperature measurements for both soot and thin filament pyrometry. Linearity and reciprocity analysis under partially saturated conditions were performed on three selected detectors and the camera response functions, which are required for HDR image reconstruction, were determined. The linearity/reciprocity of the detectors allowed the use of a simplified algorithm that was implemented to compute the HDR images; soot and flame temperature were calculated from those images by employing color-ratio pyrometry. The reciprocity analysis revealed that pixel cross talk can be a limiting factor in a detector’s HDR capabilities. The comparison with low dynamic range (LDR) results showed the advantage of the HDR approach: due to the higher SNR, the measured temperature exhibits a smoother distribution and the range is extended to lower temperature regions where the pyrometry technique starts to lose sensitivity due to detector limitations.

Design of broadband multilayer dichroic coating for a high efficiency solar energy harvesting system

Kwanil Lee, Jiachen Wang, and Sang Bae Lee

Doc ID: 235249 Received 25 Feb 2015; Accepted 17 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: We report on the design and performance of a broadband dichroic coating for a solar energy conversion system. As a spectral beam splitter, the coating facilitates a hybrid system that combines a photovoltaic cell with a thermal collector. When positioned at a 45° angle with respect to incident light, the coating provides high reflectance in the 400–1100 nm and high transmission in the 1200–2000 nm ranges for a photovoltaic cell and a thermal collector, respectively. Numerical simulations show that our design leads to a sharp transition between the reflection and transmission bands, low ripples in both bands, and slight polarization dependence.

3.15 kW direct diode-pumped near diffraction-limited all-fiber-integrated fiber laser

Hailong Yu, hanwei zhang, Haibin Lü, Xiaolin Wang, Jinyong Leng, Hu Xiao, shaofeng Guo, Pu Zhou, Xiaojun Xu, and Jinbao Chen

Doc ID: 235713 Received 05 Mar 2015; Accepted 17 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: We demonstrate a direct diode-pumped all-fiber-integrated fiber laser based on master oscillator power amplifier (MOPA) configuration at 1080 nm, producing maximum output power of 3.15 kW with corresponding optical to optical efficiency of 75.1%. Further power scaling is pump-limited and theoretical analysis demonstrates that 4kW output power can be further achieved without stimulated Raman scattering (SRS). Near diffraction-limited beam quality (M2 ~1.6 in the X and Y directions) is also achieved at the maximum output power. This compact prototype laser has excellent stability and reliability, which could benefit many practical applications, such as industrial processing.

Investigating the characteristics of TM-pass/TE-stop polarizer designed using plasmonic nanostructures

Islam Ashry, Amr Mahros, and Marwa Tharwat

Doc ID: 234795 Received 18 Feb 2015; Accepted 17 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: Plasmonics-based polarizers are important for many photonic devices and applications. In this paper, we design and investigate the characteristics of new TM-pass/TE-stop polarizer using silver nano-grating of exponentially tapered slits sidewalls. The performance of the designed polarizer are determined through monitoring the modification of its insertion loss (IL), return loss (RL), extinction ratio (ER), and far field transform due to changing its structural parameters. We find that the structural parameters of the reported polarizer such as, slit sidewalls tapering coefficient and slit openings widths have significant impacts on tuning the polarizer characteristics.

Strain field measurements around notches using SIFT features and meshless methods

Giancarlo Gonzales and Marco Antonio Meggiolaro

Doc ID: 234230 Received 09 Feb 2015; Accepted 17 Apr 2015; Posted 17 Apr 2015  View: PDF

Abstract: This work proposes a hybrid experimental-numerical technique with the aim to improve the strain measurements at stress concentration regions. The novel technique is performed employing the computer vision SIFT algorithm and meshless methods, here termed SIFT-Meshless. The SIFT is applied to perform the feature points matching in two images of the specimen surface at different stages of mechanical deformation. The output data are provided as a set of displacement measurements by tracking matched feature points. This information is then used to model both displacement and strain field on the surface by means of a meshless formulation based on the moving least squares (MLS) approximation. By applying the proposed SIFT-Meshless method, the strain distribution around a semicircular notch in a plate under bending load was investigated. The experimental results were compared to those obtained by Digital Image Correlation technique based on a subset approach and to simulations from Finite Element (FE) analysis software. The experimental results demonstrated that the present method is capable of performing reliable strain measurements at distances close to the notch where the peak strain value is expected, even in the presence of high strain gradients.

Microscopy mineral image enhancement through center operator construction

Xiangzhi Bai

Doc ID: 231764 Received 08 Jan 2015; Accepted 17 Apr 2015; Posted 17 Apr 2015  View: PDF

Abstract: Enhancing microscopy mineral image to produce clear mineral image with rich details is important for mineral analysis. To effectively enhance the microscopy mineral images, an algorithm through utilizing the constructed center operator from the opening and closing based toggle operator is proposed in this paper. Firstly, the center operator is constructed from the opening and closing based toggle operator. Secondly, the mineral image features are extracted by using the constructed center operator for mineral image enhancement. Thirdly, the multi-scale mineral image features are extracted through multi-scale morphological theory using multi-scale structuring elements. Fourthly, the final features for mineral image enhancement are constructed from the extracted multi-scale features. Finally, the mineral image is effectively enhanced through importing the final features into the original mineral image. Experimental results on various microscopy mineral images verified that the proposed algorithm performed well for mineral image enhancement and had competing performance comparing with some existed algorithms.

Subnanometer absolute displacement measurement using a frequency comb referenced dual resonance tracking Fabry-Perot interferometer

Minhao Zhu, Haoyun Wei, Shijie Zhao, Xuejian Wu, and Yan Li

Doc ID: 233108 Received 26 Jan 2015; Accepted 17 Apr 2015; Posted 17 Apr 2015  View: PDF

Abstract: Fabry-Perot (F-P) interferometry is a traceable high resolution method for displacement metrology that has no nonlinearity. Compared with the single resonance tracking (SRT) F-P interferometry, the dual resonance tracking (DRT) F-P interferometer system is able to realize tens of millimeter measurement range while maintaining the intrinsic high resolution. A DRT F-P system is thus developed for absolute displacement measurement in metrology applications. Two external cavity diode lasers (ECDL) are simultaneously locked to two resonances of a high finesse F-P cavity using the Pound-Drever-Hall locking scheme. The absolute optical frequencies of the locked ECDLs are measured using a reference diode laser, with the frequency stabilized and controlled by an optical frequency comb. The absolute cavity resonance order numbers are investigated. The measurement range is experimentally tested to achieve 20 mm, while the resolution reaches ∼10 pm level, mainly limited by the mechanical stability of the F-P cavity. Compared with the measurement results from a self-developed displacement-angle heterodyne interferometer, the displacement residuals are within 10 nm in the range of 20 mm.

Two parabolic-hyperbolic oriented partial-differential equations for denoising in electronic-speckle-pattern interferometry fringes

Chen Tang, wenjun xu, junjiang zhang, yonggang su, and KaiLeung Su

Doc ID: 231158 Received 22 Dec 2014; Accepted 17 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: The oriented partial differential equations (OPDEs)-based filtering methods have been demonstrated to be a powerful tool for denoising and yet preserving all fringes. In this paper, we propose the new oriented PDE filtering models, named the parabolic-hyperbolic oriented partial differential equations (PH-OPDEs) based on variational methods. We test the proposed PH-OPDEs on two computer-simulated and two experimentally obtained ESPI fringe patterns with poor quality and compare our models with related OPDE models. The experimental results have demonstrated that the new models have significantly better performance in the numerical stability and computational efficiency as compared with the previous oriented PDE models.

Holographic microscopy reconstruction in both object and image half spaces with undistorted 3D grid

Michel Gross, Nicolas Verrier, Daniel Alexandre, and Gilles Tessier

Doc ID: 236063 Received 11 Mar 2015; Accepted 17 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: We propose a holographic microscopy reconstruction method, which propagates the hologram, in the object half space, in the vicinity of the object. The calibration yields reconstructions with an undistorted reconstruction grid i.e. with orthogonal $x$, $y$ and $z$ axis and constant pixels pitch. The method is validated with an USAF target imaged by a $\times$60 microscope objective, whose holograms are recorded and reconstructed for different USAF locations along the longitudinal axis: -75 to +75 $\mu$m. Since the reconstruction numerical phase mask, the reference phase curvature and MO form an afocal device, the reconstruction can be interpreted as occurring equivalently in the object or in image half space.

Polarized Reflectance and Transmittance Properties of Wind-blown Sea Surfaces

Curtis Mobley

Doc ID: 233427 Received 28 Jan 2015; Accepted 16 Apr 2015; Posted 17 Apr 2015  View: PDF

Abstract: Generation of random sea surfaces using wave variance spectra and Fourier transforms is formulated so that wave energy is conserved and both wave height and slope variance are fully resolved. Monte Carlo polarized ray tracing that accounts for multiple scattering between light rays and wave facets is used to compute effective Mueller matrices for reflection and transmission of air- or water-incident polarized radiance. Irradiance reflectances computed using a Rayleigh sky radiance distribution, sea surfaces generated with Cox-Munk statistics, and unpolarized ray tracing are in error by 10-18% compared to values computed using elevation- and slope-resolving surfaces and polarized ray tracing. Radiance reflectance factors as used to estimate water-leaving radiance from measured upwelling and sky radiances are shown to depend on sky polarization, and improved values are given.

Optimized Actuators for Ultra-Thin Deformable Primary Mirrors

Sergio Pellegrino, Marie Laslandes, and Keith Patterson

Doc ID: 231885 Received 07 Jan 2015; Accepted 16 Apr 2015; Posted 17 Apr 2015  View: PDF

Abstract: A novel design and selection scheme for surface-parallel actuators for ultra-thin, lightweight mirrors is presented. The actuation system consists of electrodes printed on a continuous layer of piezoelectric material bonded to an optical-quality substrate. The electrodes provide almost full coverage of the piezoelectric layer, in order to maximize the amount of active material that is available for actuation, and their shape is optimized to maximize the correctability and stroke of the mirror for a chosen number of independent actuators and for a dominant imperfection mode. The starting point for the design of the electrodes is the observation that the correction of a figure error that has at least two planes of mirror symmetry is optimally done with twin actuators that have the same optimized shape but are rotated through a suitable angle. Additional sets of optimized twin actuators are defined by considering the intersection between the twin actuators, and hence an arbitrarily fine actuation pattern can be generated. It is shown that this approach leads to actuator systems with better performance than simple, geometrically-based actuators. Several actuator patterns to correct third-order astigmatism aberrations are presented, and an experimental demonstration of a 41-actuator mirror is also presented.

High efficiency quantum dot remote phosphor film

Shin-Tson Wu, Qi Hong, Kuo-Chang Lee, and Zhenyue Luo

Doc ID: 232339 Received 13 Jan 2015; Accepted 16 Apr 2015; Posted 17 Apr 2015  View: PDF

Abstract: We report a high efficiency quantum dot film for high color gamut edge-lit LCD backlight. On the film’s input surface, an array of asymmetric micro-prisms is used to preserve the large off-axis angle of the incident blue light. On the exit surface, the retroreflective micro-prisms retain blue light inside the film. The extended optical path effectively enhances the blue light’s probability to hit quantum dots and generate down-converted wavelengths. Without using any volume scattering particle, fewer quantum dots are needed to re-emit higher power green and red lights, which helps to lower the material cost.

Image Reconstruction Method Based on CCD Calibration in Frequency Domain

Ze Zhang, Yang He, Bin Xiangli, and Shengjun Xiong

Doc ID: 233433 Received 28 Jan 2015; Accepted 16 Apr 2015; Posted 16 Apr 2015  View: PDF

Abstract: We demonstrate a method to reconstruct CCD images by calculating out both inter- and intra- pixel response function accurately with laser interference patterns. This method is proved theoretically to have the ability of improving image quality greatly, and thus may find great applications in high-quality imaging fields.

Spot centroid sensitivity to angle of intensity on image detector with lenslet array

Mei Hui, ping zhou, Peng Su, and Zhu Zhao

Doc ID: 234092 Received 05 Feb 2015; Accepted 16 Apr 2015; Posted 16 Apr 2015  View: PDF

Abstract: Lenslet array has been introduced to detector to compensate for the low sensitivity. These lenses deviate the light from different incident angles, and potentially introduce error when sub-pixel accuracy is needed. We investigated the spot centroid position as the angle of incidence changes on Kodak KAI-16000 image detector with lenslet array, and noticed that there is a cubic dependency on the incident angle. The experiment results show that the dependence on angle of incidence is related to lenslet array in the Kodak detector used for the pentaprism test. This caused an error in spherical aberration on test surface after integration. The magnitude of the cubic component at incident angle of 14 degrees (equivalent to F/2) is 11.6 µm. It corresponds to 48 nm rms spherical aberration for the test surface and brings the scanning pentaprism test closer the principal test while there is a 56 nm rms discrepancy in them. The discrepancy in spherical aberration between the two tests reduced to 8 nm after this calibration. It also shows the contrast measurement results for Kodak detector and PointGrey detector. Experiments with two different detectors are performed to quantify this effect.

Efficient line-based lens distortion correction for complete distortion with vanishing point reprojection model

Shixiong Jiang, Danhua Cao, Yubin Wu, Song Zhu, and Pan Hu

Doc ID: 232234 Received 09 Mar 2015; Accepted 16 Apr 2015; Posted 16 Apr 2015  View: PDF

Abstract: Line-based correction method has been heavily investigated to improve the performance of lens distortion correction. However, it is difficult to achieve high-accuracy correction under the complete lens distortion (including radial, decentering and prism distortion), due to the coupling of the complete distortion parameters and the inaccuracy of line equation estimation. Here, we present a method that utilizes two models to resolve these problems, respectively. The recursive individual optimization model uses Levenberg-Marquardt (LM) to optimize each of the distortion parameters individually. And the vanishing point reprojection model improves the line equation by the known vanishing points calculated by a proposed expectation minimization (EM) algorithm. As a result, the accurate complete distortion correction can be achieved only by the line information. The validity of the proposed method was tested by some synthetic data and real images experiments. The results show that the proposed method can correct the image with the complete and non-complete distortion effectively.

One-way regular electromagnetic mode immune to backscattering

Linfang Shen, Xiaohua Deng, Lujun Hong, and Xiaodong Zheng

Doc ID: 234834 Received 17 Feb 2015; Accepted 16 Apr 2015; Posted 17 Apr 2015  View: PDF

Abstract: In this paper, we present a basic model of robust one-way electromagnetic (EM) modes at microwave frequencies, which is formed by a semi-infinite gyromagnetic yttrium-iron-garnet (YIG) with dielectric cladding terminated by a metal plate. It is shown that this system supports not only one-way surface magnetoplasmons (SMPs) but also one-way regular mode, which is guided by the mechanism of the total internal reflection. Like one-way SMPs, the one-way regular mode can be immune to backscattering, and two types of one-way modes together comprise a complete dispersion band for the system.

Terahertz spectroscopic identification of explosive and drug simulants concealed by various hiding techniques

Uroš Puc, Andreja Abina, Aleksander Zidanšek, Anton Jeglič, Gintaras Valušis, and Melita Rutar

Doc ID: 236286 Received 17 Mar 2015; Accepted 16 Apr 2015; Posted 16 Apr 2015  View: PDF

Abstract: Terahertz time-domain spectroscopy and imaging is used to study the effects of various hiding techniques on spectral features of drug and explosive simulants in combination with different paper and textile barriers. Results show that rapid detection and identification of concealed simulants is possible in the frequency range from 1.5 THz to 4.0 THz by using organic crystal based terahertz time-domain system and spectral peak analysis method.

Design and properties of a massive Coherent Amplifying Network

REMI SOULARD, Mark Quinn, and Gérard Mourou

Doc ID: 232423 Received 12 Jan 2015; Accepted 15 Apr 2015; Posted 16 Apr 2015  View: PDF

Abstract: The Coherent Amplifying Network laser is based on an array of thousands of active laser fibers coherently combined to generate high peak power pulses at high repetition rate. To achieve such a massive network, new combination architectures are presented here. They are based on implementing a spherical array of amplifying fibers thus removing the need for transport fibers from the initial scheme. These designs present an advantage in term of scalability leading to significant reduction of the temporal fluctuations compared to those of a conventional high peak power laser. Noise evolution with fiber number is calculated using a pertubative analysis of each channel parameters (phase, signal intensity, beam profile).

Image Registration under Translation and Rotation in two dimensional planes Using Fourier Slice Theorem

Mausumi Pohit and J. Sharma

Doc ID: 231649 Received 05 Jan 2015; Accepted 15 Apr 2015; Posted 16 Apr 2015  View: PDF

Abstract: Image recognition in presence of both rotation and translation is a long standing problem in correlation pattern recognition. Use of log-polar transform gives a solution to this problem, however, at a cost of losing the vital phase information from the image. The main objective of this paper is to develop an algorithm based on Fourier Slice theorem for measuring the simultaneous rotation and translation of an object in a 2D plane. The algorithm is applicable for any arbitrary object shift for full 180 ̊ rotation.

Wave transfer matrix for a spiral phase plate

Yisa Rumala

Doc ID: 233078 Received 22 Jan 2015; Accepted 15 Apr 2015; Posted 16 Apr 2015  View: PDF

Abstract: The wave transfer matrix (WTM) is applied to calculating various characteristics of a spiral phase plate (SPP) for the first time. In particular, it predicts the optical wave characteristics on input and output plane of the device when the SPP is fabricated on a substrate of the same refractive index as well as on a substrate of different refractive index compared to the SPP. The dependence of the parameters on the input laser frequency is studied in detail for a low finesse SPP etalon device for both cases. The equations derived from the WTM is used to show that a variation in input laser frequency causes the optical intensity pattern on output plane to rotate, while preserving the topology of the optical vortex, i.e. the variation in laser frequency has a minimal effect on the parameter describing the azimuthal intensity modulation and orbital angular momentum (OAM) content of the beam.

A texture orientation-based algorithm for detecting infrared maritime targets

Bin Wang, Lili Dong, Zhao Ming, Wu De, and Wenhai Xu

Doc ID: 233226 Received 26 Jan 2015; Accepted 14 Apr 2015; Posted 15 Apr 2015  View: PDF

Abstract: In infrared maritime image (IMI) taken under strong wind waves, background interferences, such as ocean waves, usually has high intensity that can easily overwhelm the brightness of small dim target, which, however, is difficult for traditional target detection algorithms to overcome. To this problem, the paper proposes a novel target detection algorithm based on texture orientation (TO). The proposed algorithm firstly analyzes the inter-subband correlation between horizontal and vertical wavelet subbands, and then, thresholding and local singularity analysis are combined to suppress background interferences. The experiment shows that, compared with traditional algorithms, the proposed one can overcome the background interferences well. Besides, in order to realize accurate target extraction, pipeline-filtering algorithm is adopted to remove background interferences completely.

A hybrid method of freeform lens design for arbitrary illumination target

Yufei Ma, Hang Zhang, Zeyu Su, Yu He, Liang Xu, Xu Liu, and Haifeng Li

Doc ID: 234465 Received 11 Feb 2015; Accepted 14 Apr 2015; Posted 15 Apr 2015  View: PDF

Abstract: We propose a hybrid method of the freeform illumination design for arbitrary target form, imposing no restriction on the boundary of the irradiance distribution. Smooth continuous surfaces and continuous irradiance distributions are achieved with two independent steps. Initial solutions of the illumination problem are obtained with the method of Supporting Paraboloids, and final solutions are acquired by solving the elliptic Monge–Ampére equations numerically. Lenses which are able to produce complex irradiance distributions can be achieved with this method and fabricated in practice. The feasibility of this approach is demonstrated by some examples with experimental results. © 2015 Optical Society of America

Surface profile measurement of a highly reflective silicon wafer by phase-shifting interferometry

YANGJIN KIM, Kenichi Hibino, Naohiko Sugita, and Mamoru Mitsuishi

Doc ID: 235738 Received 05 Mar 2015; Accepted 14 Apr 2015; Posted 14 Apr 2015  View: PDF

Abstract: In phase-shifting Fizeau interferometers, the phase-shift error and multiple-beam interference are the most common sources of systematic error affecting high-precision phase measurements. The nonsinusoidal waveforms can be minimized by applying synchronous detection with more than 4-sample. However, when the phase-shift calibration is inaccurate, these algorithms cannot eliminate the effects of nonsinusoidal characteristics. Moreover, when measuring the surface profile of highly-reflective samples, the calculated phase is critically determined not only by the decrease in the fringe contrast but also by the coupling error between the harmonics and phase-shift error. In this paper, the phase errors calculated by conventional phase-shifting algorithms were estimated by considering the coupling error. We show that the 4N – 3 algorithm, comprising the polynomial window function and the DFT term, has the smallest phase error among the conventional phase-shifting algorithms. The surface profile of the highly-reflective silicon wafer was measured using a wavelength-tuning Fizeau interferometer and the 4N – 3 algorithm.

Qualitative evaluation of Pb and Cu in fish using LIBS with multi-pulse excitation by using an ultra compact laser excitation source.

Fernando Alvira, TERESA FLORES, luis ponce, Lesther Moreira Osorio, Zeferino Perez Baez, and Geraldine Vázquez

Doc ID: 235627 Received 04 Mar 2015; Accepted 14 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: We show a new LIBS setup based on a small, ultra compact, low cost excitation source developed by the authors. The laser is a compact Nd:YAG laser emitting in multi-pulse Q-switch regime, capable of delivering a bunch of pulses with a total energy up to 300 mJ. The developed system is applied to the analysis of Pb and Cu contaminants on fish. LIBS spectra were obtained from scales, muscle and skin of both fresh and frozen samples. The developed excitation source is able to detect 0,25 and 0,20 mg/Kg of Pb and Cu respectively. In this way, the equipment seems to be adequate to achieve a screening analysis of those contaminants

Quantitative photothermal phase imaging of red blood cells using digital holographic photothermal microscope

Srivathsan Vasudevan, George Chen, Zhiping Lin, and Beng Koon Ng

Doc ID: 231595 Received 19 Jan 2015; Accepted 14 Apr 2015; Posted 14 Apr 2015  View: PDF

Abstract: Photothermal microscopy (PTM), a non-invasive pump-probe high resolution microscopy, has been applied as a bio-imaging tool in many biomedical studies. PTM utilizes conventional phase contrast microscope to obtain highly resolved photothermal images. However, phase information could not be extracted from these photothermal images as they are not quantitative. Moreover, the problem of halos inherent in conventional phase contrast microscopy need to be tackled. Hence digital holographic photothermal microscopy technique is proposed as a solution to obtain quantitative phase images. The proposed technique is demonstrated by extracting phase values of red blood cells from their photothermal images. These phase values can potentially be used to determine the temperature distribution of the photothermal images, a very important study in live cell monitoring applications.

Impact of plasma dynamics on equivalence ratio measurements by laser-induced breakdown spectroscopy

Johannes Kiefer, Bo Zhou, ZhongShan Li, and Marcus L.E. Alden

Doc ID: 232127 Received 08 Jan 2015; Accepted 14 Apr 2015; Posted 14 Apr 2015  View: PDF

Abstract: The systematic errors introduced by triggering a USB-spectrometer for LIBS equivalence ratio measurements are studied. We analyze the temporal behavior of laser-induced plasma in a non-reacting methane/air mixture and investigate the influence of the dynamics on equivalence ratio measurements with gated and ungated detection. For use of gated detectors optimal delay times were found to be between 500 and 2000 ns to allow effective suppression of interferences while maintaining sufficient signal-to-noise levels. Good precision was found for short and long exposure time intervals when an intensified CCD camera was employed. On the other hand, the jitter of an externally triggered ungated spectrometer leads to high uncertainties. Running the ungated spectrometer freely, the single-shot uncertainty can be reduced by more than one order of magnitude.

Schlieren-based temperature measurement inside the cylinder of an optical spark ignition and homogeneous charge compression ignition engine

Nikolaos Soulopoulos, Pavlos Aleiferis, Alexandros Charalambides, Yannis Hardalupas, Alex Taylor, and Yunichi Urata

Doc ID: 232294 Received 20 Jan 2015; Accepted 14 Apr 2015; Posted 14 Apr 2015  View: PDF

Abstract: Schlieren is a non-intrusive technique that can be used to detect density variations in a medium, and thus, under constant pressure and mixture concentration conditions, measure whole field temperature distributions. The objective of the current work was to design a schlieren system to measure line-of-sight averaged temperature distribution with the final aim to determine the temperature distribution inside the cylinder of Internal Combustion engines. In a preliminary step, we assess theoretically the errors arising from the data reduction used to determine temperature from a schlieren measurement and find that the total error, random and systematic, is less than 3%, for typical conditions encountered in the present experiments. A Z-type, curved-mirror schlieren system was used to measure the temperature distribution from a hot air jet in an open air environment in order to evaluate the method. Using the Abel transform, the radial distribution of the temperature was reconstructed from the line of sight measurements. There was good agreement in the peak temperature between the reconstructed schlieren and thermocouple measurements. Experiments were then conducted in a four-stroke, single-cylinder, optical spark ignition engine with a four-valve, pentroof-type cylinder head to measure the temperature distribution of the reaction zone of an iso-octane-air mixture. The engine optical windows were designed to produce parallel rays and allow accurate application of the technique. The feasibility of the method to measure temperature distributions in IC engines was evaluated with simulations of the deflection angle combined with equilibrium chemistry calculations that estimated the temperature of the reaction zone at the position of maximum ray deflection as recorded in a schlieren image. Further simulations showed that the effects of exhaust gas recirculation and air-to-fuel ratio on the schlieren images were minimal under engine conditions compared to the temperature effect. At 20 crank angle degrees before top dead centre (i.e. 20 crank angle degrees after ignition timing), the measured temperature of the flame front was in agreement with the simulations (730–1320 K depending on the shape of the flame front). Furthermore, the schlieren images identified the presence of hot gases ahead of the reaction zone due to diffusion and showed that there were no hot spots in the unburned mixture.

Near field enhancement of the nanostructure on the fused silica with rigorous method

Hu Wang, Hongji Qi, Bin Wang, Yanyan Cui, Yingjie Chai, jin yunxia, Kui Yi, and Jianda Shao

Doc ID: 233192 Received 26 Jan 2015; Accepted 14 Apr 2015; Posted 14 Apr 2015  View: PDF

Abstract: A rigorous electromagnetic method is developed to analyze the resonance effect of near field caused by nanoscale subsurface defects, which play a key role in describing absorption enhancement during laser-matter interaction for transparent dielectric materials. The total electric field calculated with this new method is in consistence with the result of finite-difference time-domain simulation. The concept of mode amplitude density spectrum is developed to analyze the specific modes of the total field. A new mode parameter is proposed to demarcate the contribution of the resonance. The frequency space is divided into four parts and the resonance effect is analyzed as well as the contributions of different modes to the total field. The influence of the structure parameters on the near field modulation and energy transference is also discussed. It is found that the enhancement mechanism of the near field and local absorption is the resonance effect caused by the total internal reflection on the side wall of the nanostructure. In addition, the surrounding energy is mainly guided into the structure by the root of the structure via the energy flow analysis.

A high-precision system identification method for deformable mirror in wavefront control

Xingkun Ma, Lei Huang, Qi Bian, Tenghao Li, Chenlu Zhou, and Mali Gong

Doc ID: 233622 Received 03 Feb 2015; Accepted 14 Apr 2015; Posted 14 Apr 2015  View: PDF

Abstract: Based on mathematic model, the relation between the accuracy of the influence matrix and the performance of the wavefront correction is established. Based on the least square method, a two-step system identification is proposed to improve the accuracy of the influence matrix, where the measurement noise can be suppressed, and the non-linearity of the deformable mirror can be compensated. The validity of the two-step system identification method is tested in the experiment, where the improvements in the precision of the wavefront correction, as well as in the efficiency of the close-loop control were observed.

An intracavity frequency-doubled and single-frequency Ti:sapphire laser with optimal length of the gain medium

Huadong Lu, Xuejun Sun, Jiao Wei, and jing su

Doc ID: 233932 Received 04 Feb 2015; Accepted 14 Apr 2015; Posted 14 Apr 2015  View: PDF

Abstract: A single-frequency 397.5 nm laser by means of intracavity frequency doubled Ti:sapphire (Ti:S) laser is presented. In order to obtain the second-harmonic generation with low threshold pump power and high out power, the optimal length of the Ti:S crystal is theoretically analyzed and experimentally measured. The experimental results are in good agreement with the theoretical expectation. After inserting the nonlinear BIBO and LBO crystals, the obtained output powers of the single-frequency 397.5 nm laser are 1.58 W and 0.78 W, respectively. At last, the tuning characteristic, power stability and beam quality are also discussed.

MCMC Sampling based Terahertz Holography Image Denoising

Qi Li and Guanghao Chen

Doc ID: 234191 Received 06 Feb 2015; Accepted 13 Apr 2015; Posted 14 Apr 2015  View: PDF

Abstract: Terahertz digital holography has attracted numerous attentions these days. This technology combines the strong transmittance of terahertz and the unique features of the digital holography. Nonetheless, the low clearness of the images captured has hampered the popularization of this imaging technique. In this paper, we try to perform digital image denoising technique on our multi-frame superposed images. The noise suppression model is concluded as Bayesian least squares estimation based on Markov chain Monte Carlo sampling (MCMC). By random walking on a weighted average filtered image, with Gaussian kernel, the MCMC based filter (MCF) keeps collecting samples, assigning them weights by similarity assessment, and constructs multiple sample sequences. Finally, these sequences are used to estimate the value of each pixel. Our algorithm shares some good qualities with Non-local Means (NLM) filtering and the algorithm based on conditional sampling (CSF) proposed by Wong et al., such as good uniformity, moreover, reveals a better performance in structure preservation, as is shown in numerical comparison using structural similarity index measurement (SSIM).

Quantitative Reflectance Spectra of Solid Powders as a Function of Particle Size

Tanya Myers, Timothy Johnson, Russell Tonkyn, Thomas Blake, Carolyn Brauer, Yin-Fong Su, Robert Richardson, and Alyssa Ertel

Doc ID: 234747 Received 18 Feb 2015; Accepted 13 Apr 2015; Posted 14 Apr 2015  View: PDF

Abstract: We have recently developed vetted methods for obtaining quantitative infrared directional-hemispherical reflectance spectra using a commercial integrating sphere. In this paper, the effects of particle size on the spectral properties are analyzed for several samples such as ammonium sulfate, calcium carbonate, and sodium sulfate as well as one organic compound, lactose. We prepared multiple size fractions for each sample and confirmed the mean sizes using optical microscopy. Most species displayed a wide range of spectral behavior depending on the mean particle size. General trends of reflectance vs. particle size are observed such as increased albedo for smaller particles: for most wavelengths, the reflectivity drops with increased size, sometimes displaying a factor of 4 or more drop in reflectivity along with a loss of spectral contrast. In the longwave infrared, several species with symmetric anions or cations exhibited reststrahlen features whose amplitude was nearly invariant with particle size, at least for intermediate- and large-sized sample fractions; that is, > ~150 μm. Trends of other types of bands (Christiansen minima, transparency features) are also investigated as well as quantitative analysis of the observed relationship between reflectance vs. particle diameter.

Single and dual-wavelength switchable linear polarized Yb3+-doped double-clad fiber laser

Liu Guanxiu and dejun feng

Doc ID: 232426 Received 12 Jan 2015; Accepted 13 Apr 2015; Posted 14 Apr 2015  View: PDF

Abstract: A single and dual-wavelength switchable linear polarized Yb-doped double-clad fiber laser is proposed, in which the resonance cavity was composed of a fiber Bragg grating fabricated in a polarization maintaining fiber and a dichromatic mirror with high reflectivity. The polarization hole burning is enhanced through selective polarization feedback by the polarization maintaining fiber Bragg grating (PM-FBG). The switchover of single and dual wavelength is realized by tuning the rotation angle of a cubic polarization beam splitter which is inserted between the dichromatic mirror and the collimator in the cavity. The laser features wavelengths of 1070.08nm and 1070.39nm, output power of 1.0 W, signal noise ratio (SNR) of 45 dB, slope efficiency of 34%, as well as a very narrow linewidth of 0.022 nm. The polarization characteristics are analyzed by measuring the laser power transmitted through a Glan-Thomson polarizer during rotation.

Tight focus of light using a micropolarizer and a microlens

Sergey Stafeev, Liam O'Faolain, Victor Kotlyar, and Anton Nalimov

Doc ID: 233134 Received 26 Jan 2015; Accepted 13 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: Using a binary microlens of diameter 14 μm and focal length 532 nm (NA = 0.997) in resist, we focus a 633-nm laser beam into a near-circular focal spot with dimensions (0.35±0.02)λ and (0.38±0.02)λ (λ is incident wavelength) at full-width of half-maximum intensity. The area of the focal spot is 0.105λ2.The incident light is a mixture of linearly and radially polarized beams generated by reflecting a linearly polarized Gaussian beam at a 100 μm x 100 μm four-sector subwavelength diffractive optical microelement with a gold coating. The focusing of a linearly polarized laser beam (the other conditions being the same) is found to produce an elliptical focal spot measuring (0.40±0.02)λ and (0.50±0.02)λ. This is the first implementation of subwavelength focusing of light using a pair of microoptic elements (a binary microlens and a micropolarizer).

Thin-film a-Si:H solar cells processed on aluminium-induced texture (AIT) glass superstrates: Prediction of light absorption enhancement

Nasim Sahraei, Ian Peters, Selvaraj Venkataraj, Armin Aberle, Sonya Calnan, Sven Ring, Bernd Stannowski, Rutger Schlatmann, and Rolf Stangl

Doc ID: 233581 Received 30 Jan 2015; Accepted 13 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: Light scattering superstrates are important for thin-film a-Si:H solar cells. In this work, aluminium-induced texture (AIT) glass, covered with non-etched Al-doped ZnO (AZO), is investigated as an alternative to the commonly used planar glass with texture-etched AZO superstrate. Four different AIT glasses with different surface roughnesses and different lateral feature sizes are investigated for their effects on light trapping in a-Si:H solar cells. For comparison, two reference superstrates are investigated as well: planar glass covered with non-etched AZO and planar glass covered with texture-etched AZO. Single-junction a Si:H solar cells are deposited onto each superstrate and the scattering properties (haze and angular resolved scattering, ARS) as well as the solar cell characteristics (current-voltage and external quantum efficiency) are measured and compared. The results indicate that AIT glass superstrates with non-etched AZO provide a similar, or even superior, light trapping than the standard reference superstrate - which is demonstrated by a higher short-circuit current Jsc and a higher external quantum efficiency. Using the trapped light fraction , a quantity based on the integrated light scattering at the AZO/a-Si:H interface, we show that Jsc depends linearly on , regardless of the type of superstrate used.

Shape estimation of diffractive optical element using high-dynamic range scatterometer

Manabu Hakko, Tomohiro Kiire, Daisuke Barada, Toyohiko Yatagai, and Yoshio Hayasaki

Doc ID: 233644 Received 03 Feb 2015; Accepted 13 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: High-dynamic range scatterometry enables us simultaneously to use weak scattered light and strong diffracted light for shape estimation of a diffractive optical element. Especially the weak scattered light is effective to identify the nanostructure in spite of having been regarded as undesirable light. We newly designed a shape estimation system based on the high-dynamic range scatterometry, composed of modeling of targets, numerical simulation of light propagation from the target, optical measurement, determination of signature region, noise reduction, data matching, and sample shape estimation. The use of the weak scattered light improved the accuracy of the shape estimation compared with using only the diffraction peaks. The validity of the shape estimation system was confirmed from the values measured by scanning electron microscope.

Photonic generation of polarization-resolved wideband chaos with time-delay concealment in three-cascaded vertical-cavity surface-emitting lasers

Huijie Liu, Nianqiang Li, and Qingchun Zhao

Doc ID: 236705 Received 23 Mar 2015; Accepted 13 Apr 2015; Posted 14 Apr 2015  View: PDF

Abstract: Optical chaos generated by chaotic lasers has been widely used in several important applications, such as chaos-based communications and high-speed random-number generators. However, these applications are susceptible to degradation by the presence of time-delay (TD) signature identified from the chaotic output. Here we propose to achieve the concealment of TD signature, along with the enhancement of chaos bandwidth, in three-cascaded vertical-cavity surface-emitting lasers (VCSELs). The cascaded system is composed of an external-cavity master VCSEL, a solitary intermediate VCSEL, and a solitary slave VCSEL. Through mapping the evolutions of TD signature and chaos bandwidth in the parameter space of the injection strength and frequency detuning, photonic generation of polarization-resolved wideband chaos with TD concealment is numerically demonstrated for wide regions of the injection parameters.

All-optical logic operation of polarized light signals in highly nonlinear silicon hybrid plasmonic microring resonators

Minming Zhang, Jing Dai, Feiya Zhou, Yuanwu Wang, Luluzi Lu, and Dengming Liu

Doc ID: 230870 Received 16 Dec 2014; Accepted 13 Apr 2015; Posted 14 Apr 2015  View: PDF

Abstract: All optical logic operation is theoretically demonstrated by means of polarization-dependent four-wave mixing (FWM) processes in a highly nonlinear silicon hybrid plasmonic waveguide (HPWG) microring resonator. We design an ultra-compact (radii=1 μm) microring resonator (MRR) realized by using silicon HPWG with the ability of subwavelength-bending. The HPWG exhibits very high confinement that can result in a remarkably high nonlinear parameter (γ~3000 W-¹m-¹), given a highly nonlinear gap material. By manipulating the polarization properties of the pump and signals with very low electric field (|E|~10⁸ Vm-¹), all optical NOT, NOR and NAND logical operations are obtained through FWM process. These compact all optical nanoplasmonic devices are stable, fabrication simplified, and silicon on insulator (SOI) compatible. Compared with intensity-dependent structures of logic operation, the polarization-dependent ones are more flexible and exhibit potential in miniaturization and integration of all-optic circuits

Compressive moving target tracking with thermal light based on complementary sampling

Wen-Kai Yu, Xu-Ri Yao, Xue-Feng Liu, Long-Zhen Li, and Guang-Jie Zhai

Doc ID: 233473 Received 29 Jan 2015; Accepted 12 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: We present a method to directly reconstruct background subtracted images using compressive ghost imaging (GI) with thermal light based on complementary modulation. Since the moving objects of interest only occupy a small portion of the field of view, i.e., they are sparse in the spatial domain, and the complementary modulation strategy makes the values of patterns in the suitable range for compressive GI reconstructions, thus with this method, we can retrieve object silhouettes and trajectory with high image quality. To demonstrate the performance of proposed protocol, we make a comparison of the mean square error. This protocol may attract general interest and be instructive for the fields of surveillance system, teleconferencing, and even search and rescue missions.

Deconvolution methods based on φHL regularization for spectral recovery

Lizhen Deng, Hu Zhu, Xiaodong Bai, Meng Li, and Zhao Cheng

Doc ID: 233793 Received 05 Feb 2015; Accepted 12 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: The recorded spectra often suffer noise and band overlapping, and deconvolution methods are always used for spectral recover. However, during the process of spectral recovery, the details always can't be preserved . To solve this problem, two regularization terms are introduced and proposed. Firstly, the conditions on the regularization term are analyzed for smoothing noise and preserving detail, and according to these conditions, φHL regularization is introduced into spectral deconvolution model. In view of the deficiency of φHL under noisy condition, adaptive φHL regularization (φAHL) is proposed. Then SBD-HL and SBD-AHL are proposed based on φHL and φAHL regularization, respectively. The simulation experimental results indicate that the proposed SBD-HL and SBD-AHL methods have better recovery, and SBD-AHL is superior to SBD-HL, especially in the noisy case.

Passively Q-switched mode-locking of Tm:YAP laser based on Cr:ZnS saturable absorber

Zhaowei Wang, Baitao Zhang, Jingliang He, Kejian Yang, Han KeZhen, Jian Ning, Jia Hou, and Fei Lou

Doc ID: 232551 Received 14 Jan 2015; Accepted 12 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: Using a Cr:ZnS wafer as the saturable absorber, a diode-pumped passively Q-switched mode-locking of Tm:YAP laser at 1976 nm has been realized for the first time, and nearly 100% modulation depth of Q-switched mode-locking was achieved. The width of the mode-locked pulse was estimated to be about 980 ps with a repetition rate of 350 MHz within an about 300 ns-long Q-switched pulse envelope. A maximum output power of 940 mW was obtained, corresponding to the Q-switched pulse energy of 0.55 mJ. The emission wavelength evolution between the continuous-wave and Q-switched mode-locked operations was presented and discussed. The experimental results indicate that the Cr:ZnS absorber is a promising saturable absorber for the passively Q-switched mode-locking operation around 2 μm.

Extremely high power CO₂ laser beam correction

Alexander Aleksandrov, Alexis Kudryashov, Vadim Samarkin, Alexey Rukosuev, Francois Chateauneuf, Pierre Galarneau, and Simon Turbide

Doc ID: 232659 Received 28 Jan 2015; Accepted 11 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: This paper presents the results of high power CO2 laser aberration correction and jitter stabilization. A bimorph deformable mirror and two tip-tilt piezo correctors were used as executive elements. Two types of wavefront sensors – one Hartmann to measure higher order aberrations (defocus, astigmatism etc.) based on uncooled microbolometer LWIR-camera, and another – the tip-tilt one based on technology of obliquely sputtered thin chromium films on Si substrates, were applied to measure wavefront aberrations. We discuss both positive and negative attributes of suggested wavefront sensors. The adaptive system allowed to reduce aberrations of income laser radiation by 7 times (P-V) and to stabilize jitter of incoming beam up to 25 μrad at a speed of 100 Hz. The adaptive system frequency range for high order aberration correction was 50 Hz.

All-optical cryptography of M-QAM formats by using two-dimensional spectrally sliced keys

Marcelo Abbade, Milorad Cvijetic, Carlos Messani, Cleiton Alves, and Stefan Tenenbaum

Doc ID: 233224 Received 04 Feb 2015; Accepted 11 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: There has been an increased interest to enhance the security of optical communications systems and networks. All-optical cryptography methods have been considered as an alternative to electronic data encryption. In this paper we propose and verify the use of a novel all-optical scheme based on cryptographic keys applied on the signal spectral for encryption of the M-QAM modulated data with bit rates of up to 200 Gb/s.

Nanometer film analysis by LIBS method: with special emphasis on the effect of laser focus to sample distance(LFTSD)

SHILEI ZHONG, Yuxiang Sun, Fukai Shan, Xin Sun, Zhe Liu, and Yuam Lu

Doc ID: 230756 Received 22 Dec 2014; Accepted 11 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: In order to develop a method to analyze the metal elements in the thin film samples rapidly, directly and without sample preparation and to understand the mechanism of laser-film interaction and plasma formation and evolution, a laboratory LIBS system was established recently for nanometer film analysis. ZrO2 films prepared on silicon chips by a sol-gel process were employed in the coming experiment and its thickness was about 40 nm. By the initial investigation we carried out, the stability of this system was verified and the relative standard deviation (RSD) of target peak is lower than 1.6% with the help of position system. The influences of different experimental parameters, such as laser energies, LFTSD settings and gate delay, were studied under the conditions of room temperature and atmospheric pressure. The experimental results showed that LFTSD was one of the most important parameters for plasma formation and spectral collection in comparison with other parameters by means of plasma spectra and images. So the effect of LFTSD on the spectra, plasma evolution and craters were specially discussed in this paper. At last,we calculated the plasma temperature and electron density under optimal parameters for quantitative analysis. The result showed that established system was available for qualitative and quantitative analysis of film under the conditions of single pulse and low ablation energy.

A simultaneous optimization method for absorption spectroscopy post-processing

Jean Simms, Xinliang An, Mack Brittelle, Varun Ramesh, Jaal Ghandi, and Scott Sanders

Doc ID: 232156 Received 08 Jan 2015; Accepted 10 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: A simultaneous optimization method is proposed for absorption spectroscopy post-processing. This method is particularly useful for thermometry measurements based on congested spectra, as commonly encountered in combustion applications of H2O absorption spectroscopy. A comparison test demonstrated that the simultaneous optimization method had greater accuracy, greater precision, and was more user-independent than the common step-wise post processing method previously used by the authors. The simultaneous optimization method was also used to process experimental data from an environmental chamber and a constant volume combustion chamber, producing results with errors on the order of only 1%.

Fiber Bragg grating ring resonators under rotation for angular velocity sensing

Carlo Edoardo Campanella, Francesco De Leonardis, and Vittorio Passaro

Doc ID: 234573 Received 12 Feb 2015; Accepted 10 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: In this paper we investigate the possibility of using hybrid resonators based on Fiber Bragg grating Ring Resonators (FBGRRs) or pi-shifted FBGRRs (i.e., defective FBGRRs) as rotation sensitive elements for gyroscope applications. In particular, we model the conventional Fiber Bragg Grating (FBG) with the Coupled Mode Theory (CMT) by taking into account how the Sagnac effect, induced by the rotation, modifies the eigenvalues, the photonic band gap and the spectral response of the FBG. Then, on the basis of the FBG model under rotation conditions, the spectral responses of the FBGRR and pi-FBGRR have been evaluated, confirming that the Sagnac effect manifests itself with a spectral shift of the eigen-solutions. This physical investigation can be exploited for opening new ways in the optical gyroscope platforms.

Mo/Si multilayer components for high harmonic generation sources

Patrick Naulleau, Eric Gullikson, Chris Anderson, Seong-Su Kim, donggun lee, Ryan Miyakawa, and Farhad Salmassi

Doc ID: 234658 Received 13 Feb 2015; Accepted 10 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: High harmonic generation (HHG) sources have made great progress over the past decade and now readily support applications in the extreme ultraviolet (EUV) regime and beyond. In many applications, key to the utility of these sources are multilayer components such as mirrors and beamsplitters. Here we present recent results in the development and fabrication of such components in the EUV regime including line-narrowing mirrors achieving bandwidths (lambda/delta_lambda) of 175, single and multiple harmonic selecting multilayers with reflectances of greater than 40% in the 13 nm range, and ultra-low stress membrane beamsplitters enabling direct EUV pulse energy monitoring.

Measurement System with High Accuracy for Laser Beam Quality

Ming Zhao, Yi Ke, Qingshan Jiang, Ke Liang, Zhen Yu Yang, Peiyuan Xie, and Ciling Zeng

Doc ID: 233879 Received 04 Feb 2015; Accepted 10 Apr 2015; Posted 29 Apr 2015  View: PDF

Abstract: Presently most of the laser beam quality measurement system collimates the optical path manually with low efficiency and low repeatability. To solve these problems, this paper proposed a new collimated method to improve the reliability and accuracy of the measurement results. The system accuracy controlled the position of the mirror to change laser beam propagation direction, which can realize the beam perpendicularly incident to the photosurface of camera. The experiment results show that the proposed system has a good repeatability and the measuring deviation of M2 factor is less than 0.6%.

Linear polarization optimized Stokes polarimeter based on four-quadrant detector

Hui Ma, Chao He, Jintao Chang, Yong Wang, Ran Liao, Honghui He, and Nan Zeng

Doc ID: 232790 Received 19 Jan 2015; Accepted 09 Apr 2015; Posted 16 Apr 2015  View: PDF

Abstract: A four-quadrant detector (4QD) consists of four well balanced detectors. We report a Stokes polarimeter with optimal linear polarization measurements based on a 4QD. We turned the four intensity detection channels into four polarization analyzing channels by placing four polarizers and one quarter wave plate in front of the individual detectors. An optimization method for the four polarization analyzing channels is proposed to improve the measurement accuracy. Considering applications in favor of linear polarization measurements instead of global optimization for all the possible states of polarizations (SOPs), we optimize the polarimeter first for the linear polarization components, then for the circular polarization component. The polarimeter is capable of simultaneous measurements of fast varying SOPs with improved performance for the linear polarizations.


Yuliana Espinosa-Sánchez, Donato Luna-Moreno, and David Monzón

Doc ID: 235630 Received 04 Mar 2015; Accepted 09 Apr 2015; Posted 16 Apr 2015  View: PDF

Abstract: For an expert nose the aroma of a beverage is a fingerprint, which can be used to certify its authenticity, distinguish between distillation processes or even identify the raw material used to fabricate it. In this work we propose a simple, automatic, and repeatable optical method that can be used as a first and quick test to authenticate tequila samples. This method is based on the measurement of the beam intensity changes, using the surface plasmon resonance (SPR) technique, operating at a fixed angle. We observed that each tequila, depending on the alcohol contents and the aging process, produces a specific change in intensity level measured.

Ultracompact Tapered Coupler for the Si/III-V Heterogeneous Integration

Huang Qiangsheng, jianxin cheng, Liu Liu, Yongbo Tang, and Sailing He

Doc ID: 232367 Received 20 Jan 2015; Accepted 08 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: An ultracompact tapered coupler, which is suitable for mode transformation between a 220nm-high silicon wire waveguide and a Si/III-V hybrid waveguide, is proposed for Si/III-V heterogeneous integration. The tapered coupler is composed of three sections. Since the tapered coupler avoids exciting the unwanted high-order modes in the III-V waveguide, the length of the tapered coupler can be dramatically shortened. In the proposed structure, the total length of the tri-sectional tapered coupler can be as short as 8 μm with a fundamental mode-coupling efficiency of over 95% in a bandwidth of over 100 nm. The alignment tolerance of the proposed structure is also analyzed.

Line shape of amplitude or frequency-modulated spectral profiles including resonator distortions

Martin Suter and Martin Quack

Doc ID: 230690 Received 12 Dec 2014; Accepted 07 Apr 2015; Posted 09 Apr 2015  View: PDF

Abstract: We report experiments and an improved method of analysis for any harmonics of frequency-modulated spectral line shapes allowing for very precise determinations of the resonance frequency of single absorption lines for gigahertz spectroscopy in the gas phase. Resonator perturbations are implemented into the formalism of modulation spectroscopy by means of a full complex transmission function being able to model the asymmetrically distorted absorption line shapes for arbitrary modulation depths, modulation frequencies and resonator reflectivites. Exact equations of the in-phase and the quadrature modulation signal, taking into account a full resonator transmission function, are simultaneously adjusted to two channel lock-in data performed in the gigahertz regime to obtain the spectral line position. The determination of the absorption line position of the rotational transition\\ $J^{\prime} =7 \leftarrow J^{\prime\prime}=6$ of $^{16}$O$^{12}$C$^{32}$S in the vibrational ground state is investigated while changing the resonator distortions. The results are subjected to the approach proposed here and compared to standard methods known from the literature.

Time resolved combination of the Mueller-Stokes and Jones calculus for the optimization of a twisted-nematic spatial light modulator

Mathias Krüger, Ronald Kampmann, Roman Kleindienst, and Stefan Sinzinger

Doc ID: 232082 Received 13 Jan 2015; Accepted 07 Apr 2015; Posted 08 Apr 2015  View: PDF

Abstract: Twisted-Nematic spatial light modulators (TN-SLM) show a coupling between phase and intensity modulation. We present quick and simple methods for characterizing the modulator’s optical properties. We utilize a combination of the Mueller-Stokes and Jones calculus to adapt the polarization configuration in the optical system for phase-only modulation. Furthermore we investigate the Flicker-effect and propose a novel method which completely compensates its temporal influence while optimizing the modulation properties. Although we applied our methods to a HOLOEYE LC-R 2500 they can be generalized for the application with any liquid crystal spatial light modulator.

Research of Two Dimensional Beam Steering in LCOS-based WSS

Dongtang Yang, Cheng He, Zean Jing, and Fengguang Luo

Doc ID: 232515 Received 19 Jan 2015; Accepted 07 Apr 2015; Posted 08 Apr 2015  View: PDF

Abstract: Phenomenon of two dimensional beam steering in liquid crystal on silicon (LCOS) is demonstrated. We propose a novel flexible wavelength selective switch (WSS) using LCOS two dimensional beam steering. The cross-talk of adjacent channel in the WSS is theoretically small, while the measured insert loss is lower than 15dB.

Infrared and visible image fusion using multiscale directional nonlocal means filter

Xiang Yan, Hanlin Qin, Jia Li, Huixin Zhou, Jing-guo Zong, and Qingjie Zeng

Doc ID: 233260 Received 28 Jan 2015; Accepted 07 Apr 2015; Posted 08 Apr 2015  View: PDF

Abstract: Fusion of infrared and visible images is a significant research area in image analysis and computer vision. The purpose of infrared and visible images fusion is to combine the complementary image information of the source images into a fused image. Thus, it is vital to efficiently represent the important image information of the source images and choose rational fusion rules. To achieve the aim, an image fusion method using multiscale directional nonlocal means filter (MDNLM) is proposed in this paper. The MDNLM combines the feature of preserving edge information by the nonlocal means filter with the capacity of capturing directional of image information by directional filter bank, which can effectively represent the intrinsic geometrical structure of images. The MDNLM is a multiscale, multidirectional and shift-invariant image decomposition method, and we use it to fuse infrared and visible images in this paper. First, the MDNLM is discussed and used to decompose the source images into approximation subbands and directional detail subbands. Then, the approximation and directional detail subbands are fused by a local neighborhood gradient weighted fusion rule and a local eighth order correlation fusion rule, respectively. Finally, the fused image can be obtained through the inverse MDNLM. Comparison experiments have been performed on different image sets, and the results clearly demonstrate that the proposed method is superior to some conventional and recent proposed fusion methods in terms of the visual effects and objective evaluation.

Research on Measuring Polarization State of Light by Stokes Parameters Based on Electro-optic effect

Shaojun lu, Chunmin Zhang, and jun han

Doc ID: 235828 Received 09 Mar 2015; Accepted 07 Apr 2015; Posted 08 Apr 2015  View: PDF

Abstract: The polarization information of light can be used to improve the possibility of target recognization. Stokes parameters can express all kinds of polarization states comparing with Jones matrix. So many ways have been developed to measure light polarization state by Stokes parameters. But traditional systems meet challenges in stability and velocity. A new method was proposed in this paper to apply LiNbO3 crystal as phase retarder in replacing wave plate. It has the merits of static without moving elements and rapid measurement. The transversal electro-optic effect is exploited to avoid the high voltage loaded on LiNbO3 crystal. Four different voltages were loaded on four LiNbO3 crystals respectively to obtain four values of related phase difference and four intensity values recorded on the detector one time, from which the Stokes parameters of the detected light can be obtained to express the light polarization state. This system has the possibility to measure high speed changing polarized light even less than microseconds. The experiments were performed to prove the feasibility of this proposed method. The calculated polarization state is close to expected Stokes parameters for the linearly and circularly polarized light. It is suitable for the fields demanding stably and real-time monitoring the changing of polarization state.

Simulation design of a wearable see-through retina projector

Cheun-Lin Tien, Wen-Shing Sun, Yen-Chen Chiang, and Jui Wen Pan

Doc ID: 228325 Received 04 Dec 2014; Accepted 06 Apr 2015; Posted 09 Apr 2015  View: PDF

Abstract: This study proposes a new design of a wearable see-through retina projector combined with a compact camera. The see-through retina projector is composed of illumination and imaging system. Our design for eyeglasses would project all this information directly into the user's eyes using a see-through retina projector. The retina projector images a 20 inch upright virtual image at 2 m in front of human eyes, and the illumination system provides uniform illumination for liquid crystal on silicon panels. Moreover, RGB LED array is used as the light source to generate color images with color sequential. The compact camera is a lens with the aperture F/2.8, the angle-of-view 30 degree, and 2 million pixels. Such an optical system design with the combination of a see-through retina projector and a compact camera presents the volume about 5.83 cm3 and the weight 6.02 g.

Modeling and implementation of a fiber based quartz-enhanced photoacoustic spectroscopy system

Chunsheng Yan, Jian Chen, Yongjiang Dong, Sailing He, Longqiang Luo, and Erik Forsberg

Doc ID: 233394 Received 28 Jan 2015; Accepted 06 Apr 2015; Posted 09 Apr 2015  View: PDF

Abstract: A compact fiber based quartz enhanced photoacoustic spectroscopy system requiring no extra optical lens has been developed for the detection of acetylene. The system is based on a common fiber or an axicon fiber to conduct the light. Experimental results shows comparable detection sensitivity to that of tapered fiber based photoacoustic spectroscopy systems. The system is easy to adjust and has low insertion loss and is thus well suited for small portable sensor applications in the future. A numerical model based on actual beam profiles was furthermore developed as part of the study to investigate the optimal positions of the fibers and to verify the experimental results.

2D Laser Feature Extraction Based on Improved SEF

BU YAN, Zhang Hua, Wang Heng, Ran Liu, and Kinpeng Wang

Doc ID: 233493 Received 04 Feb 2015; Accepted 03 Apr 2015; Posted 10 Apr 2015  View: PDF

Abstract: SEF (Successive Edge Following) has been widely used to describe the environmental characteristics based on two-dimensional (2D) laser range finder due to its simplicity. However, the segmentation accuracy of the regular SEF for different distances is very low. And besides that, the regular SEF sometimes fails to characterize the corner features in the continuous segmentation. To solve these problems, we propose an improved SEF approach, which combines 2D polar radius-arc, adaptive threshold in region to divides different radius data into groups more reasonably. Region growing is also discussed to localize the corner based on variance of segmentation and its fitting. Finally, all features described by line segments are used to build the map. As compared to the traditional SEF, our approach is information-lossless. Our experimental results show that the segmentation accuracy is improved while the segmentation number is reduced and the feature detection accuracy is increased respectively, as compared with the regular SEF.

(ISSR2014)GPU accelerated parallel FFT processing for Fourier transform hyperspectral imaging

Jianping Li and Yi Xiao

Doc ID: 225904 Received 31 Oct 2014; Accepted 02 Apr 2015; Posted 02 Apr 2015  View: PDF

Abstract: Sequentially processing massive 1-dimension fast Fourier transformations (FFT) on raw interferograms using CPU has limited the speed of conventional Fourier transform imaging spectrometers (FTIS). This paper reports the implementation of highly paralleled FFT computation using low-end graphics processing unit (GPU) device for acceleration of this process. Comparison experiment results have demonstrated ~10-30 times acceleration improvement using the GPU-based parallel processing over conventional CPU-based serial processing upon the input data with same sizes; GPU processing time of only 630ms and 173ms of datacubes with 512×512×1024 and 64×64×16k pixels respectively has presented its potential for on-line and even real-time FTIS raw data processing. The addition of a cheap GPU device into any FTIS system involves no optical modifications, so it is a highly cost-effective technique for temporal resolution enhancement of FTIS based hyperspectral imaging applications.

(ISSR2014) Functional NIR Imaging Reconstruction based on Spatio-Temporal feature: Venous Occlusion Studies

Anuradha Godavarty, Young-Jin Jung, and Jean Gonzalez

Doc ID: 228311 Received 24 Nov 2014; Accepted 02 Apr 2015; Posted 02 Apr 2015  View: PDF

Abstract: Non-contact based near-infrared (NIR) optical imaging devices are developed for non-invasive tissues imaging in various clinical applications. Most of these devices focus on obtaining the spatial information for identification of blood vessels as in sub-surface vein localization applications. In the current study, the spatio-temporal mapping of blood vessels based on functional information was performed using NIR optical imaging without the use of external contrast agents. A 710 nm LED source and a compact NIR sensitive CCD camera system were employed during simple cuff (0 to 60 mmHg) experiment in order to acquire the dynamic NIR data from the dorsum of a hand. The spatio-temporal features of dynamic NIR data were extracted from the cuff experimental data to localize vessel according to blood dynamics. The blood vessels’ structure reconstructed from the dynamic data based on the spatio-temporal features. Demonstrating the spatio-temporal feature of blood dynamic imaging using a portable non-contact NIR imaging device without external contrast agents is significant for applications such as peripheral vascular diseases and wound screening.

Spatial acquisition scheme with ultrawide FOV for atmospheric optical links: based on fisheye lens and sinusoidal amplitude grating

Xuelian Ma

Doc ID: 229259 Received 09 Dec 2014; Accepted 02 Apr 2015; Posted 02 Apr 2015  View: PDF

Abstract: We present a spatial acquisition scheme based on fisheye lens and sinusoidal amplitude grating, which can acquire laser beacons in ultrawide field of view (FOV) for atmospheric optical links. In this scheme, an incoming laser beacon can be imaged into three diffraction spots. The laser direction and the wavelength can be measured from the center position of the spots and the distance between two adjacent spots, respectively. The total optical transfer function (OTF) can be described by the combined effect of acquisition system itself and spatial coherence degradation due to atmospheric turbulence. Spot spread and spot dancing effects are both considered for long-term exposure and short-term exposure. We investigate how rms (root mean square) errors of the measured laser direction and wavelength vary with the ratio of pupil diameter D2 to atmospheric coherence length r0, without consideration of aberrations of the fisheye lens. Results show that with the limitation of r0, the performance cannot be infinitely improved by enlarging D2. When considering aberrations of the fisheye lens, the imaged spot is gradually blurred and deteriorated with the increase of the field angle, since aberrations are enlarged with the increase of the field angle. We study how the measured errors of laser direction and wavelength vary with r0 and incident angles (with different aberrations). A severe turbulence with a small value of r0 and a large incident angle will cause a bad acquisition performance.

Optical loading sensor based on ring-cavity fiber laser incorporating a 45°-tilted fiber polarizing grating

Zhongyuan Sun, Chengbo Mou, Zhijun Yan, Kaiming Zhou, Xiangchuan Wang, Jianfeng Li, and Lin Zhang

Doc ID: 232904 Received 21 Jan 2015; Accepted 01 Apr 2015; Posted 08 Apr 2015  View: PDF

Abstract: We have experimentally demonstrated an active loading sensor system based on a fiber ring laser with single-polarization output using an intra-cavity 45°-tilted fiber grating (45°-TFG). When the laser cavity fiber is subjected to loading, the laser output is encoded with the loading information that can be measured and monitored by a standard power meter. The achieved loading sensitivity is 0.033/ (kg•m-1) and 0.042/ (kg•m-1) for two different interaction lengths. The experimental results clearly show that such a single polarization fiber laser may be developed to a low-cost high-sensitivity loading sensor system.

Zernike power spectra of clear and cloudy light-polluted urban night skies

Salvador Bara Vinas, Víctor Tilve, Miguel Nievas, Alejandro Sanchez de Miguel, and Jaime Zamorano

Doc ID: 231318 Received 23 Dec 2014; Accepted 28 Mar 2015; Posted 30 Mar 2015  View: PDF

Abstract: The Zernike power spectra of the all-sky night brightness distributions of clear and cloudy nights are computed using a modal projection approach. The results obtained in the B, V and R Johnson-Cousins' photometric bands during a one-year campaign of observations at a light-polluted urban site show that these spectra can be described by simple power laws with exponents close to -3 for clear nights and -2 for cloudy ones. The second-moment matrices of the Zernike coefficients show relevant correlations between modes. The multiplicative role of the cloud cover, that contributes to a significant increase of the brightness of the urban night sky in comparison with the values obtained in clear nights, is described in the Zernike space.

A Scalable Design for a High Energy Cryogenic Gas Cooled Diode Pumped Laser Amplifier

Paul Mason, Michael Fitton, Andrew Lintern, Saumyabrata Banerjee, Klaus Ertel, Tristan Davenne, John Hill, Steve Blake, Paul Phillips, Thomas Butcher, Jodie Smith, Mariastefania De Vido, Justin Greenhalgh, Cristina Hernandez-Gomez, and John Collier

Doc ID: 233909 Received 04 Feb 2015; Accepted 28 Mar 2015; Posted 31 Mar 2015  View: PDF

Abstract: In this paper we present details of a scalable design for a cryogenic helium gas cooled DPSSL amplifier based on a multi-slab Yb:YAG geometry, capable of efficient amplification of nanosecond pulses to kJ pulse energies at repetition rates of 10 Hz and beyond. A scaled-down prototype amplifier design capable of amplifying 10 ns pulses to 10 J at 10 Hz is presented derived from computational fluid dynamic calculations and thermal modelling. Model predictions have also been used to design a suitable cryogenic gas cooling system, details of which are also presented. Experimental testing has confirmed stable amplifier temperatures are achievable from room temperature down to 88 K, with a gas coolant temperature stability of ± 0.2 K. Single-pass transmission wave front measurements are in reasonable agreement with model predictions derived from thermal maps for two different YAG slab geometries. Slabs with a narrower width Cr-doped YAG absorptive cladding, added to suppress ASE, demonstrated a wave front error of ~0.2 waves at 1030 nm (peak-to-valley) over the 20 mm x 20 mm pumped region within the amplifier. The low level of optical distortion confirms that the amplifier design provides an acceptable level of temperature and flow uniformity and demonstrates the merit of a multi-slab geometry.

Iterative phase retrieval algorithms: Part II. Attacking optical encryption systems

John Sheridan, Changliang Guo, and Shi Liu

Doc ID: 232605 Received 20 Jan 2015; Accepted 24 Mar 2015; Posted 24 Mar 2015  View: PDF

Abstract: The modified iterative phase retrieval algorithms developed in Part I [1] are applied to perform known plaintext and ciphertext attacks (KPCA) on both Amplitude Encoding (AE) and Phase Encoding (PE) Fourier transform based Double Random Phase Encryption (DRPE) systems. It is shown that the new algorithms can retrieve the two Random Phase Keys (RPKs) perfectly. The performances of the algorithms are tested by using the retrieved RPKs to decrypt a set of different ciphertexts encrypted using the same RPKs. Significantly, it is also shown that the DRPE system is, under certain conditions, vulnerable to Ciphertext-Only Attack (COA), i.e. in some cases an attacker can decrypt DRPE data successfully when only the ciphertext is intercepted.

Calibration of Fourier domain short coherence interferometer for absolute distance measurements

Risto Montonen, Ivan Kassamakov, Edward Hæggström, and Kenneth Österberg

Doc ID: 234122 Received 10 Feb 2015; Accepted 16 Mar 2015; Posted 17 Mar 2015  View: PDF

Abstract: We calibrated and determined the measurement uncertainty of a custom made Fourier domain short coherence interferometer operated in laboratory conditions. We compared the optical thickness of two thickness standards and three cover slips determined with our interferometer to the geometric thickness determined by SEM. Using this calibration data we derived a calibration function C = (0.017r – 0.1) µm with a 95% confidence level system uncertainty of (5.9 × 10-3r + 2.3) µm, where r is the optical distance in µm, across the 240 µm optical measurement range. The confidence limit includes contributions from uncertainties in the optical thickness, geometric thickness, and refractive index measurements as well as uncertainties arising from cosine errors and thermal expansion. The results show feasibility for non-contacting absolute distance characterization with micron-level accuracy. This instrument is intended for verifying the alignment of the discs of an accelerating structure in the possible future Compact LInear Collider.

Theoretical and experimental investigation of singly resonant optical oparametric oscillator under double-pass pumping

Kuanshou Zhang, Peng Li, Yuanji Li, and JinXia Feng

Doc ID: 234012 Received 04 Feb 2015; Accepted 15 Mar 2015; Posted 16 Mar 2015  View: PDF

Abstract: The singly resonant optical parametric oscillator (SRO) under double-pass pumping in a two-mirror linear cavity is investigated theoretically and experimentally. Different output couplers are used in the periodically poled lithium niobate based SRO to optimize the extracted signal output. When the 2.5% output coupler is used, the pump threshold as low as 3.7 W is achieved, and 6.2 W of signal at 1.56 µm with the linewidth of 62.5 kHz is obtained at pump power of 14.5 W. The measured signal frequency drift and peak-to-peak power fluctuation are less than ±40 MHz and ±0.9% in a given 1 hour, respectively.

Nanometer level characterization of JWST optomechanical systems using high speed interferometry

David Chaney, Babak Saif, W. Smith, Perry Greenfield, Warren Hack, Austin Van Otten, Joshua Bluth, Marcel Bluth, Tony Sanders, Ritva Keski-Kuha, Lee Feinberg, Michael North Morris, and James Millard

Doc ID: 231818 Received 07 Jan 2015; Accepted 20 Feb 2015; Posted 25 Mar 2015  View: PDF

Abstract: The James Webb Space Telescope Optical Telescope Element (OTE) is a three mirror anastigmat consisting of a 6.5 m segmented primary mirror (PM), a secondary mirror (SM) and a tertiary mirror. The primary mirror comprises 18 individual hexagonal segments. The telescope and instruments will be assembled at Goddard Space Flight Center (GSFC) to build the Optical Telescope Element-Integrated Science Instrument Module (OTIS). While at GSFC, the OTIS will go through a series of environmental tests. In these tests the OTIS will be exposed to launch level acoustics and vibration. To assure that OTIS’s performance has not changed due to these environmental tests, the assembly be tested optically at the Center of Curvature (CoC) of the PM. A high speed interferometer (HSI) has been designed and built to characterize both static and dynamic changes due to environmental exposure. This paper describes the details of these measurement techniques. To validate and develop the techniques that will be used on OTIS assembly two spare JWST PM segments were measured and the results presented here.

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