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Accepted papers to appear in an upcoming issue

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Dispersion spectroscopy with optical frequency combbasedsingle-shot dual-heterodyne mixing

NASRIN SULTANA, Hiroali Tada, Leona Yuda, and Tatsutoshi Shioda

Doc ID: 371122 Received 26 Jun 2019; Accepted 16 Oct 2019; Posted 16 Oct 2019  View: PDF

Abstract: We present a novel approach to high-speed dispersion spectroscopy that realizes a wide dynamic range, bysimultaneous and parallel phase measurement using scan-less dual-heterodyne mixing of 50- and 1.4 GHzfrequency intervals. This system can realize parallel measurements of the relative phases between adjacentfrequencies by introducing an optical frequency comb and intensity modulator to generate adjacent frequency andarrayed waveguide grating to separate the sidebands. The experimental results using single-mode fibers, whoselengths range from 0 to 92 km, indicated a 26 nm dispersion spectrum, 1785 ps∕nm measurement range, and 0.27ps∕nm measurement uncertainty in 1 ms.

Remote Raman Spectroscopy of Natural Rocks

Genesis Berlanga, Tayro Acosta-Maeda, Shiv Sharma, John Porter, Przemyslaw Dera, Hannah Shelton, Jeffrey Taylor, and Anupam Misra

Doc ID: 373009 Received 18 Jul 2019; Accepted 16 Oct 2019; Posted 16 Oct 2019  View: PDF

Abstract: We report remote Raman spectra of natural igneous, metamorphic, and sedimentary rock samples at a standoffdistance of 5 m. High quality remote Raman spectra of unprepared rocks are necessary for accurate and realisticanalysis of future Raman measurements on planetary surfaces such as Mars. Our results display the ability of aportable Compact Remote Raman System (CRRS) to effectively detect and isolate various light and dark-coloredmineral phases in natural rocks. The CRRS easily detected plagioclase and potassium feldspar end members,quartz, and calcite in rocks with high fluorescence backgrounds. Intermediate feldspars and quartz, when found inrocks with complex mineralogies, exhibited band shifts and broadening in the 504-510 cm-1 and 600-1200 cm-1regions. A good approximation of intermediate plagioclase feldspars was possible by using overall Raman spectralshape and assigning other minor Raman peaks in addition to the 504-510 cm-1 peaks. Detection of olivine andpyroxene in mafic rocks allowed for compositional characterization.

Improving the Spectral Qualities of Major Elements in Soil by Controlling the Ambient Pressure in Time-Resolved Laser-Induced Breakdown Spectroscopy

Rongxing Yi, Xinyan Yang, Fangrui Lin, and Sheng Ren

Doc ID: 378310 Received 20 Sep 2019; Accepted 16 Oct 2019; Posted 16 Oct 2019  View: PDF

Abstract: Laser-induced breakdown spectroscopy (LIBS) is a powerful tool in the soil monitoring field, but the poor spectral quality limits its application. To improve the spectral quality of major elements in soil samples, a method based on controlling the ambient pressure and time sequence was introduced. Spectral qualities which include signal to background ratio (SBR), spectral stability and spectral profile were all studied in different ambient pressures and delay times. The results show the SBRs of Na and K elements increased about 5 times, when the air pressure and delay time were controlled. Meanwhile, the relative standard deviations (RSDs) were improved from more than 30% to less than 5% due to the release of the self-absorption effect. This work proved that the spectral qualities of LIBS can be improved a lot by controlling the ambient pressure in the field of detecting major elements in soil.

Optimal mass transportation problem in the design offreeform optical elements generating far-fieldirradiance distributions for plane incident beam

Dmitry Bykov, Leonid Doskolovich, Albert Mingazov, and Evgeni Bezus

Doc ID: 378508 Received 19 Sep 2019; Accepted 16 Oct 2019; Posted 16 Oct 2019  View: PDF

Abstract: We consider the problem of calculating a refracting surface generating a prescribed irradiance distributionin the far field in the case of a plane incident beam. We demonstrate that this problem can be formulatedas a mass transportation problem (MTP) and obtain the cost function for the MTP. It is shown that witha special choice of coordinates, the cost function becomes quadratic. The obtained mass transportationproblem also describes the problem of calculating a mirror, which can be considered as a special caseof the problem of calculating a refracting surface. We propose a method of calculating a refracting surfacebased on the reduction of the MTP to a linear assignment problem. This method is applied to thedesign of several optical elements generating prescribed intensity distributions. The simulation resultsdemonstrate high performance of the proposed approach.

Holographic Waveguide HUD with in-line pupil expansion and 2D FOV expansion

Colton Bigler, Micah Mann, and Pierre-Alexandre Blanche

Doc ID: 373853 Received 26 Jul 2019; Accepted 15 Oct 2019; Posted 16 Oct 2019  View: PDF

Abstract: A method of head-up display is presented that uses an in-line surface relief grating attached to a waveguide propagation head-up display to achieve a large field of view without the need for large projection optics. Horizontal pupil expansion is achieved using an extraction hologram that is multiple times the size of the injection hologram and is recorded with modulated diffraction efficiency. Vertical pupil expansion is achieved by coupling the surface relief grating to the waveguide surface between the injection and extraction holograms. The grating replicates the beam along the propagation direction, which allows for a larger field of view at the extraction. Using this technique, both a Zemax OpticStudio computer model and a physical system demonstrator achieve a field of view of 16x14.25 degrees.

Three-dimensional microscopic imaging throughscattering media based on in-line phase-shift digitalholography

Shutaro Kodama, Manami Ohta, Kanami Ikeda, Yutaka Kano, Yoko Miyamoto, Wolfgang Osten, Mitsuo Takeda, and Eriko Watanabe

Doc ID: 372482 Received 16 Jul 2019; Accepted 15 Oct 2019; Posted 16 Oct 2019  View: PDF

Abstract: Microscopic three-dimensional imaging and phase quantification for objects hidden behind a scattering medium byusing in-line phase-shift digital holography are proposed. A spatial resolution of 1.81 μm and highly accuratequantitative phase imaging are demonstrated for objects behind a scatter plate. Three-dimensional imaging wasconfirmed using objects with a depth difference of 1.32 mm. Further, imaging was performed using rat skin as ademonstration for imaging through complex multi-layer scattering medium, where a spatial resolution close totheoretically predicted value was achieved by experiment.

Centred camera based effective perspectiveimages’ segmentation and mosaicking method(CCEPISM) for full parallax holographicstereogram printing

Fan Fan, Xingpeng Yan, Xiaoyu Jiang, Teng Zhang, Jun Wen, Jian Su, Quan Yuan, Xi Wang, Song Chen, and Chao Han

Doc ID: 374447 Received 06 Aug 2019; Accepted 15 Oct 2019; Posted 15 Oct 2019  View: PDF

Abstract: The centred camera based effective perspective images’ segmentation and mosaickingmethod (CCEPISM) is proposed to improve the previous EPISM based printing of full parallaxholographic stereogram. The idea of the pixel mapping from target camera images to centredcamera images is analyzed, and the backward pixel mapping as well as the forward pixelmapping is modeled and formulated to transform the perspective images captured by differentcamera strategies. The principle of the proposed CCEPISM are introduced in detail alongwith its specific implementation. The experimental results validate the proposed method anddemonstrate that CCEPISM is an effective way for the printing of full parallax holographicstereogram, and the quality of optical reconstruction is the same as that of the EPISM basedholographic stereogram, the whole 3D scene is captured by centred camera image, the pixelswaste caused by simple-camera-capture and the number of the sampled perspective images arereduced significantly.

Comparison studies of the Scheimpflug lidartechnique and the pulsed lidar technique foratmospheric aerosol sensing

Liang Mei, Teng Ma, Zheng Kong, Zhenfeng Gong, and Hui Li

Doc ID: 375724 Received 21 Aug 2019; Accepted 15 Oct 2019; Posted 15 Oct 2019  View: PDF

Abstract: The Scheimpflug lidar (SLidar) technique has been recently developed for variousremote sensing applications, where the lidar signal is detected by an image sensor accordingto the Scheimpflug principle instead of the time-of-flight principle. Comparison studiesbetween the SLidar technique and the conventional pulsed lidar technique are crucial forunderstanding the principle as well as the measurement results of the SLidar technique. In thiswork, a 520-nm Scheimpflug lidar system and a 532-nm pulsed lidar system have beendeveloped for comparison studies. Atmospheric remote measurements as well as statisticalanalysis have been carried out on a near horizontal path and on a slant direction with anelevation angle of 30°. The temporal-spatial variations of the atmospheric backscatteringmaps measured by the 520-nm SLidar system and the 532-nm pulsed lidar system generallyagreed well. The median extinction coefficient measured by the SLidar and the pulsedtechniques has shown similar temporal evolution during the near-horizontal comparisonstudy, and a correlation coefficient of 0.99 has been achieved through statistical analysis onall lidar measurements. Moreover, the root mean square error (RMSE) ratio for eachextinction coefficient profiles has also been evaluated, and the mean value of the RMSE ratiofor all lidar measurements was about 11% in homogeneous atmospheric conditions. Duringslant comparison studies, the RMSE ratio between the SLidar curve and the pulsed lidar curvewas less than 5% in the region of 0.5-2 km, and it generally increased with the increasing ofthe measurement distance primarily due to the decreased range resolution of the SLidartechnique. The promising results suggested that the SLidar technique, featuring of short blindrange, could be suitable for aerosol sensing particularly in the planetary boundary layer.

An effective method for further magnifying theimage in holographic projection under divergentlight illumination

pang hui, Axiu Cao, wen Liu, Lifang Shi, and Qiling Deng

Doc ID: 376105 Received 22 Aug 2019; Accepted 15 Oct 2019; Posted 15 Oct 2019  View: PDF

Abstract: Divergent light illumination can effectively increase the diffraction angle of holographicprojection. However, the achieved maximum image size is limited to the geometric enlargement of thehologram size with the existing double-sampling Fresnel diffraction algorithm. In this paper, aneffective method for further magnifying the image is proposed. The theoretical maximum size underdivergent illumination is first analyzed. On this basis, a virtual intermediate plane is introducedbetween the source plane and the image plane. Then three-step diffraction calculation is performed toevaluate the Fresnel diffraction between the hologram plane and the image plane, so that the samplinginterval on the image plane is related to the position of the virtual plane and can be flexibly tuned.Consequently, the achieved image size can be further enlarged. The feasibility of the proposed methodis demonstrated by simulations and experiments.

Multifocal multi-value phase zone plate for 3Dfocusing

Shima Gharbi Ghebjagh, David Fischer, and Stefan Sinzinger

Doc ID: 376618 Received 05 Sep 2019; Accepted 15 Oct 2019; Posted 15 Oct 2019  View: PDF

Abstract: We demonstrate a method for creating three-dimensional (3D) array of focal spots by combination of a multi-focaldiffractive lens and a two-dimensional multi-value phase grating. The multi-focal Fresnel -based lens is created bymeans of encoding special nonlinearities into the phase structure of a Fresnel zone plate and is represented as amathematical superposition of this phase function with a refractive lens. The imposed nonlinearity type enablesthe creation of multiple focal spots with uniform intensity along the optical axis. We demonstrate the example of a3D multi-value phase grating which creates five focal planes with a 5×5 transverse array of focal spots with equalenergy distribution, in each plane. Experimental results are included to verify the theoretical outcomes, where thephase pattern of 3D multi-value phase grating is encoded onto a spatial light modulator (SLM).

Dual-wavelength TEM01 mode passively mode-locked Nd:YAGlaser with SESAM

Ning Wen, LongPu Li, Zong Nan, Tu Wei, Ke Liu, zhimin wang, Yong Bo, qinjun peng, Da Cui, and Xu Zuyan

Doc ID: 376788 Received 30 Aug 2019; Accepted 15 Oct 2019; Posted 15 Oct 2019  View: PDF

Abstract: A dual-wavelength TEM01 mode synchronous continuous wave passively mode-locked (CWML) Nd:YAG laserhas been demonstrated with a semiconductor saturable absorber mirror (SESAM) at 1319 and 1338 nm for thefirst time to our knowledge. The maximum average output power 10.84 W was obtained at 113.8 W absorbedpump power, corresponding to an optical to optical conversion efficiency of 9.5%. The dual-wavelength CWMLpulses had a pulse duration of 35.1 ps at a repetition rate of 76 MHz. The beam quality was measured to beM2=2.51.

Increase in efficacy of near-infraredfemtosecond micromachining in ophthalmichydrogels with the addition of sodiumfluorescein, rose bengal, and riboflavin

Sara Campaign and Wayne Knox

Doc ID: 375694 Received 16 Aug 2019; Accepted 14 Oct 2019; Posted 15 Oct 2019  View: PDF

Abstract: We report on the effect of exogenous doping agents with large two-photonabsorption cross-sections on the efficacy of near-infrared femtosecond micromachining inophthalmic hydrogels. Contaflex GM Advance 58 hydrogels were solution doped in lowconcentrations of sodium fluorescein, rose bengal, and riboflavin dissolved in balanced saltsolution prior to femtosecond micromachining with three near-infrared wavelengths: 720 nm,800 nm, and 1035 nm. Using any of the three doping agents in the concentrations studiedproduced an increase in the amount of optical phase change induced in the material at allwriting wavelengths and reduced the amount of power needed to induce a desired amount ofphase change.

Accurate Detection of Small Particles in DigitalHolography using Fully Convolutional Networks

Xuecheng Wu, Xinwen Li, Longchao Yao, Yingchun Wu, Xiaodan Lin, Linghong Chen, and Kefa Cen

Doc ID: 372724 Received 16 Jul 2019; Accepted 14 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: Particle detection is a key procedure in particle field characterization with digital holography. Due to variousbackground noises, spurious small particles might be generated and real small particles might be lost duringparticle detection, therefore, accurate small particle detection remains a challenge in the research of energy andcombustion. A deep learning method based on modified fully convolutional networks is proposed to detect smallopaque particles (e.g., coal particles) on extended focus images. The model is tested by several experiments andproved to have good small particle detection accuracy.

Phase-Shifting Digital Holographic Microscopy withIterative Blind Reconstruction Algorithm

Ana Doblas, Carlos Buitrago-Duque, Aaron Robinson, and Jorge Garcia-Sucerquia

Doc ID: 372731 Received 16 Jul 2019; Accepted 14 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: In phase-shifting digital holographic microscopy (PS-DHM), the reconstructed phase map is obtained afterprocessing several holograms of the same scene with a phase shift between them. Most of the reconstructionalgorithms in PS-DHM require an accurate and known phase shift between the recorded holograms. Thisrequirement limits the applicability of the method. To ease the use of PS-DHM, this paper presents an iterativeblindphase shift extraction method based on the demodulation of the different components of the recordedholograms. The method uses a DHM system operating in a slightly off-axis architecture. The proposed method usesthree-frame holograms with arbitrary and unequal phase-shifts between them and therefore eases the use of thePS-DHM. Both simulated and experimental results demonstrate the goodness and feasibility of the proposedtechnique.

High-repetition rate injection seeded Nd:YVO4 lasersby high-speed intracavity phase modulation

Xuezhe Cao, Peilin Li, and Qiang Liu

Doc ID: 377477 Received 09 Sep 2019; Accepted 14 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: We demonstrate high-repetition rate injection seeded Q-switched Nd:YVO4 ring lasers operating at 5 kHz and 10kHz. The frequency of the lasers is stabilized by the fast ramp-fire technique based on a RbTiOPO4 (RTP)intracavity phase modulator. At 5 kHz, the highest output energy of 1.5 mJ is achieved with a pulse duration of 8.1ns, a frequency jitter of 1.7 MHz/min, and a linewidth of 71 MHz. The corresponding values at 10 kHz are 0.7 mJ,12.1 ns, 1.9 MHz/min, and 45 MHz, respectively. The short-term timing stability is 15 ns. The performance of thelasers demonstrates that the high-speed ramp-fire technique with the intracavity phase modulator is especiallyappropriate to obtain stable Fourier-transform-limited single frequency operation of high-repetition rate injectionseeded lasers.

The evolution of the Raman beam quality in a foldedcoupled-cavity Nd:YVO4/YVO4 Raman laser

Jingbo Wang, Xin Ding, Jian Liu, Guizhong Zhang, Xuanyi Yu, Sun Bing, Yang Liu, Tengteng Li, Yuntao Bai, Lei Zhao, Guoxin Jiang, Peng Lei, Liang Wu, and Jian-Quan Yao

Doc ID: 377570 Received 11 Sep 2019; Accepted 14 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: An end-pumped actively Q-switched Nd:YVO4/YVO4 Raman laser with a folded coupled cavity is demonstrated tostudy the evolution of Raman beam quality. The theoretical mechanism of beam cleanup effect of stimulatedRaman scattering (SRS) is analyzed. The beam quality (M2) of the Raman beam and the fundamental beams beforeand after the Raman conversion are measured experimentally. The results show that with the incident pumppower increasing, the M2of the fundamental beam increases from 1.85 to 3.08 while the M2of Raman beamincreases from 1.21 to 1.69. The beam quality of the Raman laser and its degradation are better than that of thefundamental laser.

Preparation and characterization ofnanosphere and nanorod Gd2O3:Tb3+ by polyolroute

MEIGUI OU, Huina Qiao, Rong Fu, Yanyan Hu, Chunlin Yang, and Hao Yin

Doc ID: 367485 Received 13 May 2019; Accepted 14 Oct 2019; Posted 15 Oct 2019  View: PDF

Abstract: Nanorods and nanospheres Gd2O3:Tb3+ particles were synthesized from chlorideprecursors GdCl3 and TbCl3 by NaOH addition in diethylene glycol (DEG) medium. Thenanospheres and the nanorods of Gd2O3:Tb3+ were tuneably obtained by adjusting theaddition speed of NaOH. The structure, morphologies and the luminescence properties ofnanorods and nanospheres Gd2O3:Tb3+ were characterized by X-ray diffraction(XRD),scanning electron microscopy (SEM), transmission electron microscopy(TEM), fluorescencespectrometer, respectively. The results confirmed that the structure of nanorods andnanospheres Gd2O3:Tb3+ is cubic Gd2O3, and the luminescence of nanospheres is moreintense than that of nanorods. The low cytotoxicity measured by MTT method indicated thatthe good biocompatibility of the samples.

Fixed Window Aggregation AD_Census algorithm for Phase-based Stereo Matching

shengming zhang, Mingxiong Wu, Yanxue Wu, Gaoxu Wu, and Fei Liu

Doc ID: 372041 Received 12 Jul 2019; Accepted 14 Oct 2019; Posted 15 Oct 2019  View: PDF

Abstract: Phase-based Stereo Matching (PSM) is a vital step in binocular structured light. PSM is hard to strike a balance between efficiency and accuracy, especially because of Absolute Phase Matrix’s(APM) double data type. It means that PSM needs more run time and memory than conventional intensity images’ stereo matching. In this paper, we propose a modified AD-Census algorithm named as Fixed Window Aggregation AD-Census (FWA-AD-Census) to balance the contradiction between efficiency and accuracy in PSM. The FWA-AD-Census aggregates matching cost in a fixed support window instead of adaptive support window in AD-Census. We analyze the reason why PSM is more suitable to aggregate matching cost in a fixed support window. Simulations and experiments are conducted to verify the FWA-AD-Census’s performances by comparing FWA-AD-Census with two other local stereo matching algorithms. One is AD-Census, which is more accurate but less efficient. Its matching cost is aggregated in an adaptive support window. Another is SAD, which is more efficient but less accurate and its matching cost is aggregated in a fixed support window. Theoretical analysis and experimental results both indicate that the proposed algorithm can achieve similar accuracy to AD-Census with less run time.

A novel dynamic calibration method of the laser beamfor non-orthogonal shaft laser theodolitemeasurement system

Fengjin Miao, bin wu, congcong peng, and gaoju ma

Doc ID: 375158 Received 14 Aug 2019; Accepted 13 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: The non-orthogonal shaft laser theodolite (N-theodolite) measurement system is a new kind of instrument appliedto the large-scale metrology. The system consists of two identical N-theodolites, each of which is made up of atwo-dimensional rotary table and one collimated laser respectively. The three axes of the N-theodolite have nostrict requirements on their orthogonality and intersection conditions. A novel method is proposed to calibrateN-theodolite measurement system, and the calibration method of the laser beam for N-theodolite is the keyinnovation aspect of this paper. The laser beam is calibrated through rotating dynamically. Through theexperiment, the straightness accuracy of the laser beam of the left N-theodolite is 0.08mm and the rightN-theodolite is 0.074mm. The repeatability of the straightness accuracy is ±0.032mm. The uncertainty of straightnessaccuracy is 0.040mm. Measurent experiment results show that maximum deviation of the measured value of thissystem is 0.34mm at a range of 5 m, which is verified to be a feasible method for the calibration of the laser beam.

Comparison of photoemission performance of GaAsphotocathode between white light andmonochromatic light illumination during activation

Cheng Feng, Jian Liu, Yijun Zhang, Yunsheng Qian, Yufei Song, Yongqiang Bao, and Jing Zhao

Doc ID: 375190 Received 12 Aug 2019; Accepted 13 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: To obtain higher quantum efficiency and longer operational lifetime of negative-electron-affinity GaAs-basedphotocathode, illumination conditions using different light source during activation process are explored. GaAsphotocathodes were activated under white light and 633nm monochromatic light with different intensities, andexperimental quantum efficiencies and photocurrent degradations are compared after activation and recesiations.The results show that GaAs photocathode can obtain higher quantum efficiency and longer lifetime by usingillumination of 633nm monochromatic light, and this advantage can hardly be achieved by adjusting intensities ofwhite light. This work verifies an improved solution for preparing GaAs-based photocathodes with satisfactorycapability.

Absolute metrology method of the X-raymirror with speckle scanning technique

Lian Xue, Zhongliang Li, Tunhe Zhou, Xiaohao Dong, Hongxin Luo, Hongchang Wang, Kawal Sawhney, and Jie Wang

Doc ID: 375937 Received 20 Aug 2019; Accepted 13 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: As an important characterization method for beamline optics, at-wavelengthmetrology technology based on wavefront measurements has been developed for many years.However, the previous studies on at-wavelength metrology of reflective mirrors is limited tothe indirect method. So, the accurate surface information of the mirror under test wouldnormally be inaccessible because of lack of experimental deconvolution between the mirrorand any backgrounds from upstream optics. In this study, an absolute metrology method isdeveloped based on the speckle scanning technique. Using this method, the surface profile ofthe mirror can be extracted exactly from the mixed information of the entire upstreambeamline. At the same, data acquisition time can also be significantly reduced by theprocessing algorithm introduced in this study without sacrificing the angular sensitivity.

Highly sensitive optical fiber curvature sensor basedon a seven-core fiber with a twisted structure

Weijuan Chen, Zhihao Chen, Yishen Qiu, Lingxin Kong, Hanqing Lin, Chuanzheng Jia, Huibin Chen, and Hui Li

Doc ID: 376112 Received 23 Aug 2019; Accepted 13 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: A highly sensitive Mach-Zehnder interferometer based on a twisted structure in seven-core fiber (SCF) forcurvature measurement is investigated both theoretically and experimentally. The device is fabricated by splicinga segment of a twisted SCF with single mode fibers by over fusion method. An interference pattern of the straightsensor appears apparently in the transmission spectra. When the sensor is bent, the wavelength shift of theinterference pattern is induced, which may be used for curvature measurement through wavelength shift. In theexperiment, SCFs with and without the twisted structure are tested and the results are compared with wavelengthbasedsensitivities. The proposed twisted-SCF sensor offers a maximum curvature sensitivity of -25.16 nm/m–1within the measurement range of 0.5201 m-1-1.0071 m-1, which is a 37- fold improvement by comparing with theprevious works. The results also indicate that this highly sensitive all-fiber sensor offers a great potential forrealization of curvature measurement in the field of structural health monitoring.

Structural design method of the meridionallobster-eye lens with optimal efficiency

Mingzhao Ouyang, Xuan Zhao, Wenjun He, Liangxin Yang, Yuan Hu, Yeming Han, Shizhang Ma, and Yuegang Fu

Doc ID: 374080 Received 06 Aug 2019; Accepted 13 Oct 2019; Posted 16 Oct 2019  View: PDF

Abstract: Lobster-eye optics has been proposed as a high-energy detection device with greatpotential for astronomical observation and safety inspection since its large field of view (FOV)focusing ability. In this paper, we study the relationship between the optimal structural parametersof the meridional lobster-eye lens and the focusing efficiency. The maximum odd reflectioncomponent which only relates to the FOV and the channel ratio of depth to width has been found.Furthermore, the structural constant C which determines the optimal efficiency structure of themeridional lobster-eye lens is revealed for hard X-ray. Meanwhile, by introducing the accuratereflectivity of Iridium in soft X-ray, the constraint of the effective FOV with respect to the X-raywavelength is analyzed. The research results can help to design the optimal structure of thelobster-eye lens in multiple spectrums.

Simulation of relief-type diffractive lenses in ZEMAX using parametric modelling and scalar diffraction

Anna Nemes-Czopf, Dániel Bercsényi, and Gabor Erdei

Doc ID: 373604 Received 24 Jul 2019; Accepted 12 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: For the simulation of relief-type diffractive surfaces an efficient method has been developed and described. Based on zone-decomposition, our approach maps the transmitted wavefront by ray-tracing, while PSF/MTF plots are calculated by scalar diffraction, taking light diffracted into multiple orders into account inherently. Using a parametric user-defined surface, our solution makes the analysis and optimization of diffractive lenses possible directly inside optical design software. Implementation was carried out in ZEMAX in the form of a swift DLL extension using an approximative, non-iterative algorithm. The average computation time increment relative to standard built-in surfaces is 38% and 21% for PSF and MTF calculations, respectively. Application of our method is illustrated by the analysis of diffractive intraocular lenses. For validation, numerical results were compared with analytical formulae and industry-standard measurements. The ray-tracing error caused by our approximation proved to be less than 7∙10−6 wavelength, difference from theoretical MTF calculations is 1-2%. The RMS difference of simulated-measured through-focus MTF values at 50 lp/mm is 0.031, equaling 2σ measuring accuracy.

Measurement of cloud particles in cloudchamber based on interference technology

Jinlu Sun, Zhonghao Li, Ping Tian, Reijie Li, Dagong Jia, T. Liu, and Hongxia Zhang

Doc ID: 376450 Received 05 Sep 2019; Accepted 12 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: Based on interference technology, a cloud particle measurement system isdesigned. The scattering angle of the system is selected as 90°. The iterative mean filteralgorithm is modified and the system testing using laboratory measurement is completed.The measurement of the spectral distribution of warm cloud particles in a cloud chamber isrealized. Similar particle-size distributions are observed under different pressures, and theparticle size is mainly distributed in the range of 5 μm to 50 μm. The peak appears atparticle sizes of 20 μm to 30 μm. This system features potential applications in cloudmicrophysics research.

Fractal spiral zone plate with high-order harmonicssuppression

Huaping Zang, shuangling ding, lai Wei, Chuanke Wang, Quanping Fan, and leifeng cao

Doc ID: 369454 Received 06 Jun 2019; Accepted 12 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: We extend the concept of fractal spiral zone plates and define a new family of Cantor sequence spiral zone plates(CSSZPs) by removing the interference of high-order harmonics. In this typical design, apart from combining thespiral zone plates and Cantor fractal structure together, the desired physical properties have been realized byusing a two-parameter modified sinusoidal apodization window along the azimuthal direction to eliminate thehigh-order harmonics. Numerical simulation reveals that the intensity of high diffraction orders of the CSSZPs canbe effectively suppressed by at least three orders of magnitude while the shapes of sequence of focused opticalvortices surrounding the first primary focal length are maintained, similar as that of the fractal spiral zone plates.The demonstration experiment based on spatial light modulator has been also carried out to confirm the desiredcharacteristics. This new kind of diffractive elements may offers potential alternative for 3D optical tweezers,optical imaging, and lithography.

Inversion of two flux and four flux radiativetransfer models for determining scatteringand absorption coefficients for a suspendedparticle device

David Barrios, Carlos Alvarez, Jose Miguitama, Daniel Gallego, and Gunnar Niklasson

Doc ID: 371275 Received 28 Jun 2019; Accepted 12 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: Intrinsic and extrinsic scattering and absorption coefficients of a suspended particledevice (SPD) smart window sample at dark and clear appearance states –without and withapplied electrical voltage respectively– were determined by means of the Maheu, Letoulouzanand Gouesbet four-flux (intrinsic) and Kubelka-Munk two-flux (extrinsic) radiative transfermodels, respectively. Extrinsic values were obtained from fits to the two-flux model takinginto account the predominantly forward scattering of the SPD. As an approximation, theFresnel reflection coefficients were integrated out to the critical angle of total internalreflection, in order to compute diffuse interface reflectances. Intrinsic coefficients wereretrieved by adding a new proposed approximation for the average crossing parameter, basedon the collimated and diffuse light intensities at each interface. This approximation, althoughan improvement of previous approaches, is not entirely consistent with the two-flux modelresults. However, it paves the way for further development of methods to solve the inverseproblem of the four-flux model.

On-board Spectral Calibration Algorithm forAirborne Hyperspectral Imager andElimination of the Effect of AtmosphericUnderlying Surface

Honglin Liu, Yueming WANG, and Zhang Dong

Doc ID: 373479 Received 24 Jul 2019; Accepted 11 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: As an image-spectrum merging technology, hyperspectral sensor has become animportant part of the remote sensing scientific fields. The spectral calibration results of thehyperspectral sensor measured in laboratory should be refined when applied to the on-boardimaging spectrometer due to variations between the laboratory and actual flight environments.The larger the spectrum offset of spectral response function (SRF), the worse the retrievalaccuracy of the reflective characteristics of the targets. Therefore, an on-board spectralcalibration algorithm based on standard diffuse boards with a gradient of reflectivity isproposed in this paper. By constructing the differential function of radiation transfercoefficients, the center wavelength offsets of SRF can be solved. In addition, a BP (BackPropagation) neural network has been established to eliminate the effect of atmosphericunderlying surface and improve the accuracy of on-board spectral calibration. The threesigmaconfidence interval of the on-board spectral precision is ±0. nm (uncertainty < 0.05spectral pixels). The algorithm can be applied to a general hyperspectral sensor.

An improved spherical mirror multipass cell basedinterband cascade laser spectrometer for detectingambient formaldehyde at pptv levels

Bo Fang, Nana Yang, Weixiong Zhao, Chunhui Wang, Weijun Zhang, Wei Song, Dean Venables, and Weidong Chen

Doc ID: 374556 Received 02 Aug 2019; Accepted 10 Oct 2019; Posted 10 Oct 2019  View: PDF

Abstract: We report the development of an improved spherical mirror multipass cell based interband cascade laser (ICL)spectrometer for ambient formaldehyde (HCHO) detection. The multipass cell consists of two easily manufacturedspherical mirrors which are low-cost and have a simple structure, large mirror area utilization, and dense spotpattern. Optical interference caused by the multipath cell was largely reduced, resulting in good sensitivity. Usingwavelength modulation spectroscopy (WMS), a detection precision (1σ) of 51 pptv in 10 s was achieved with anabsorption path length of 96 m, which compared favorably with the performance of other state-of-the-artinstruments. The precision can be further improved by using a long absorption path length configuration and byremoving fringe-like optical noise caused by the collimatation lens. Ambient application of the developedspectrometer was demonstrated.

Design of all-solid W-type index fluorotelluritefibers with near-zero-flattened chromaticdispersion for optical frequency comb generation

Yali Huang, Ningning Zhou, Qing Li, Zhixu Jia, Fei Wang, WP Qin, Da-Ming Zhang, and Guanshi Qin

Doc ID: 372154 Received 09 Jul 2019; Accepted 10 Oct 2019; Posted 11 Oct 2019  View: PDF

Abstract: All-solid W-type index fluorotellurite fibers (AWFTFs) with near-zero-flatteneddispersion (NZFD) profiles are designed for optical frequency comb (OFC) generation. Thefiber core and cladding materials are TeO2–BaF2–Y2O3 (TBY) and fluoroaluminate glasses,respectively. Those two glasses have large refractive index contrast, similar thermalexpansion coefficients and softening temperatures. The zero-dispersion wavelength of theTBY glass is about 2517 nm. By introducing fluoroaluminate glasses with relatively lowrefractive index as the cladding material and controlling the core diameter, the zerodispersionwavelength of the fiber is shifted from 2517 nm to the wavelength region of 1500–1600 nm. Furthermore, two layers of thin annular glasses including fluoroaluminate glassbasedinter layer and TBY glass-based outer layer are added around the fiber core, whichmakes the fiber have a flat dispersion profile in the wavelength range of 1500–1600 nm. Byoptimizing the parameters (the core diameter, the thickness of the thin annular glass, etc.) ofAWFTFs, the fiber with the chromatic dispersion value between −0.2 and 0.35 ps/nm/km inthe wavelength range of 1500–1600 nm is achieved. To investigate the application of theAWFTFs for OFC generation via cascaded four-wave mixing, we perform numericalsimulations. The simulated results show that flat-top OFC spectrum expanding from 1450 to1700 nm with tunable mode spacing from 25 to 100 GHz can be generated in 2-m-long fiberby using a 1550-nm laser with a pulse width of 0.825 ps and a peak power of 60 W as thepump source.

Spatial coherence mapping of structured sources: aflexible instrument for solar studies

Tiago Magalhães and Jose Rebordao

Doc ID: 373157 Received 19 Jul 2019; Accepted 10 Oct 2019; Posted 11 Oct 2019  View: PDF

Abstract: We conceptually describe and design, to first-order, an instrument to locally map the spatial coherence ofextended and structured sources, such as fiber bundles or the Sun, considered as a mosaic of individualsolar cells - which is our main motivation. Our Solar Coherence Instrument, or SCI, is an instrument foran afocal solar space telescope, the light from its exit pupil, dynamically selects one individual solar cellat a time and performs a series of Young-like experiments with different baselines in order to measurethe spectral degree of coherence and, therefore, the effective correlation length that can be assigned forthat solar cell. SCI requests flexibility, in terms of selective imaging and Young experiments, which isprovided by two Digital Micromirror Devices (DMD), a technology currently under space qualification.SCI is a compact instrument based on rectroreflections, and generates all data required to image the source,to select the cells and to implement sequentially a series of Young apertures on a re-imaged pupil. Itwas designed using the (already launched) Hinode Solar Optical Telescope as a baseline, and the firstestimation of the SNR, using commercial DMDs and array sensors, while measuring the modulation ofYoung interference fringes, validates our first-order design.

Morphological and damage growthcharacteristics of shell-type damage of fusedsilica optics induced by UV laser pulses

Ke Wang, Bin Ma, Jiaqi Han, Hongfei Jiao, Xinbin Cheng, and Zhanshan Wang

Doc ID: 374276 Received 01 Aug 2019; Accepted 10 Oct 2019; Posted 11 Oct 2019  View: PDF

Abstract: Under the radiation of nanosecond pulse laser, the types of damage and damageprofile of fused silica optics are closely related to the surface and subsurface defects of thecomponent. Using raster scanning mode to measure the laser-induced damage threshold offused silica optics, three different types and sizes of damage patterns are found, of which shelldamage is the intermediate state of three types and is a bridge connecting submicron sizedamage and catastrophic damage. This paper mainly studies the mechanism and damagegrowth law of shell damage, analyzes the model of laser-induced shell damage, and discussesthe probability and cause of shell damage growth.

Noise optimization of erbium-ytterbium co-doped fiber amplifier through annealing effect

Baoluo Yan, Haifeng Liu, Bo Liu, Lin Wei, Jianguo Liu, Hao Zhang, Chang Jin Li, Xiaolong Li, and Yujia Wang

Doc ID: 372097 Received 09 Jul 2019; Accepted 09 Oct 2019; Posted 10 Oct 2019  View: PDF

Abstract: In the past few years, although annealing effect equips optical fibers or fiber amplifiers with excellent power recovery features after post-treatment processing, their noise feature has not yet been sufficiently investigated. Thanks to the recovery of partial color centers (especially the Yb2+ center) through photo-bleaching, the absorption of seed signal light due to the presence of color centers is weakened and the sensitized path of the irradiated erbium-ytterbium co-doped fiber amplifier (EYDFA) is partially restored, which help to suppress amplified spontaneous emission and increase the gain of the EYDFA as well. Thermal annealing process is performed by the first amplification stage of the EYDFA, and the increase in the optical signal-to-noise ratio of the signal light indicates that our proposed scheme could be also exploited to further improve the output performances of the EYDFA. This work is anticipated to open up new prospects for future optical communications systems based on pre-amplification technology.

Spatially multiplexed picosecond pulse-train generation in a 6-LP-mode fiber based on multiple four-wave-mixings

haisu zhang, Marianne Bigot, Pierre Sillard, and Julien Fatome

Doc ID: 373655 Received 24 Jul 2019; Accepted 09 Oct 2019; Posted 10 Oct 2019  View: PDF

Abstract: We report on the generation of four spatially multiplexed picosecond 40-GHz pulse trains in a km-long 6-LP multimode optical fiber. The principle of operation is based on the parallel nonlinear compression of initial beat-signals into well separated pulse trains owing to intra-modal multiple four-wave mixings. A series of four 40-GHz dual-frequency beatings at different wavelengths are simultaneously injected into the LP01, LP11, LP02 and LP12 modes of a 1.8-km long graded-index few-mode fiber. The combined effects of Kerr nonlinearity and anomalous chromatic dispersion lead to the simultaneous generation of four spatially multiplexed Kerr frequency combs which correspond in the temporal domain to the compression of these beat-signals into picosecond pulses. The temporal profiles of the output pulse-trains demultiplexed from each spatial mode show that well-separated picosecond pulses with negligible pedestals are then generated.

Structural modification of transparent materials with band gap by laser radiation at the absorption edge

Alexander Grigorev

Doc ID: 371970 Received 08 Jul 2019; Accepted 09 Oct 2019; Posted 09 Oct 2019  View: PDF

Abstract: Now, the problem of control over the process of structural modification of transparent materials by laser radiation is of a great practical interest. This work proposes the novel method of the controllable modification of a material structure, which uses the laser pulses with wavelength at the material fundamental absorption edge. The method is based on the effect of thermal shift of the semiconductor absorption edge. The structure modifies by local heating of the material with laser pulses focused inside a transparent semiconductor. The laser heating process was investigated numerically and experimentally, that allowed us to determine the conditions under which the preset increase in temperature occurs in the local material area. As was clarified, the heating is a threshold process and can be of two spatial structures: spot-like and line-like. The proposed method provides temperature changes in a large range. Therefore, the method can be applied for realizing different structural modifications. This has multiple applications in practical tasks such as the optical recording of information, the formation of various photonic or others microstructures with complicated topology inside transparent materials, the dividing semiconductor wafers into chips.

Assessment of speckle denoising filters for digitalholography using subjective and objective evaluationmodels

Elsa Fonseca, Paulo Fiadeiro, Marco Bernardo, António Pinheiro, and Manuela Pereira

Doc ID: 372861 Received 16 Jul 2019; Accepted 08 Oct 2019; Posted 09 Oct 2019  View: PDF

Abstract: Digital holography is an emerging imaging technique for displaying and sensing three dimensional objects.The perceived image quality of a hologram is frequently corrupted by speckle noise due to coherentillumination. Although several speckle noise reduction methods have been developed so far, there arescarce quality assessment studies to address their performance and they typically focus solely on objectivemetrics. However, these metrics do not reflect the visual quality perceived by a human observer.In this work, the performance of four speckle reduction algorithms, namely the nonlocal means, the Lee,the Frost and the block matching 3D filters, with varying parameterizations, were subjectively evaluated.The results were ranked with respect to the perceived image quality to obtain the mean opinionscores using pairwise comparison. The correlation between the subjective results and twenty differentno-reference objective quality metrics was evaluated.The experiment indicates that block matching 3D and Lee are the preferred filters, depending on hologramcharacteristics. The best performing objective metrics were identified for each filter.

Design, Optimisation and Performanceevaluation of GSST clad low-loss non-volatileswitches

Junchao Song, SOUVIK GHOSH, Hanyu Zhang, Linjie Zhou, and Azizur Rahman

Doc ID: 376224 Received 26 Aug 2019; Accepted 08 Oct 2019; Posted 09 Oct 2019  View: PDF

Abstract: In this paper, we investigate performance of a self-sustained ON-OFF switch incorporating anew phase change material Ge2Sb2Se4Te1 with Silicon rib waveguide at thetelecommunication wavelength 1.55 μm. A full-vectorial H-field finite element method isused to find effective index and modal loss of the quasi-TE modes in GSST-Si waveguide.Both the electro-refraction and electro-absorption type design are studied and the effect ofGSST thickness and Si slab thickness on the device performances are presented. These resultssuggest that a GSST-Si rib waveguide with a 500 nm wide Si core, 60-90 nm Si slabthickness, and 40-60 nm GSST layer could be a realistic switch design which can yield a verycompact, 5 μm long device with only 0.135 dB total insertion loss and more than 20 dBextinction ratio.

A modeling study of scattering and absorption properties of tar-ball aggregates

Michael Mishchenko and Li Liu

Doc ID: 376732 Received 29 Aug 2019; Accepted 08 Oct 2019; Posted 09 Oct 2019  View: PDF

Abstract: Atmospheric tar balls (TBs) form an important class of atmospheric brown carbon (BrC) particulates. The morphology of the individual TBs is typically described as amorphous and nearly spherical. However, several studies reported observations of TBs aggregated with other aerosols or agglomerations consisting of up to tens of individual TBs. We use the superposition T-matrix method to compute the scattering matrix elements and optical cross sections for a variety of TB aggregates each of which is composed of a number of monomers whose sizes follow a log normal distribution. The results for a TB aggregate can differ fundamentally from those calculated for two simplified models commonly used in climate modeling, viz., the external mixture of TBs and the respective volume-equivalent sphere model. Clustering of individual TBs into an aggregate can either enhance or weaken absorption depending on the wavelength, the monomer size, and how absorptive the BrC material is. In the case of strongly absorptive BrC, aggregation results in enhanced absorption only at 1064 nm, while at 355 and 532 nm TB aggregates become less effective absorbers relative to the corresponding external mixtures. The effect of aggregation is always to increase the single-scattering albedo and asymmetry parameter, sometimes more than tenfold. The significant scattering-matrix differences between a TB aggregate, the “equivalent” external mixture, and the volume-equivalent sphere model demonstrate the failure of the conventional Lorenz–Mie theory to represent the scattering properties of morphologically complex BrC aerosols. We show that TB aggregates can help explain exceptionally strong and spectrally dependent lidar depolarization ratios reported in several recent studies.

PHASE-RETRIEVAL METHOD FOR MEASURING SMALLCONTACT ANGLES OF PENTANE ON WATER

Sarit Feldman, Eli Raz, and Stephen Lipson

Doc ID: 370769 Received 24 Jun 2019; Accepted 08 Oct 2019; Posted 09 Oct 2019  View: PDF

Abstract: Pentane drops on a water surface are predicted to have contact angles of the orderof one degree or less in the phase of frustrated complete wetting. We have developed anoptical method of measuring such small contact angles, applicable to cases where therefractive indices of the substrate and adsorbate are very similar and the fluid dynamics do notallow delay between image acquisitions, by using phase retrieval to map the surface profile ofthe drops. It is empirically shown that with our method a difference of nanometer order can beachieved for the phase-retrieved dimensions relative to their expected value. Results agreewith numerical predictions by Weiss and Widom (2001).

Holographic Amplification of the DiffractionAngle from Optical Phase Array for OpticalBeam Steering

Colton Bigler, Zachary Rovig, Joshua McDonald, and Pierre-Alexandre Blanche

Doc ID: 372007 Received 08 Jul 2019; Accepted 08 Oct 2019; Posted 08 Oct 2019  View: PDF

Abstract: Beam steering in LIDAR applications presents an important engineering problem,as researchers seek to achieve the highest possible field of view with low energy cost and rapidrefresh rate. Non-mechanical beam steering technologies that exist today are known to achievea low energy cost and rapid refresh rate, but they have a narrow angular range. A method bywhich the diffraction angle from a beam steering device may be increased to cover a 4 sr solidangle is presented. Multiple holograms are recorded in the same volume hologram in a processcalled multiplexing. This multiplexed hologram can diffract light over a solid angle of 2 sr. Toincrease the angular coverage up to 4 sr, a hemispheric lens is attached to the volume hologram.Secondary holographic optical elements coated on the lens surface further diffract the light,directing it to a theoretical maximum of 4 sr. An early prototype demonstrates five distinctdiffraction angles, ranging from 20 to 150, which covers a solid angle around 90% of the entiresphere while maintaining beam collimation.

2D/3D Mixed Display Based on Integral Imagingand Switchable Diffuser Element

Ren Hui, Yan Xing, Han-Le Zhang, Qiang Li, Lei Wang, Huan Deng, and Qiong-Hua Wang

Doc ID: 372689 Received 15 Jul 2019; Accepted 08 Oct 2019; Posted 08 Oct 2019  View: PDF

Abstract: In this paper, we present a 2D/3D mixed system with high image quality based on integralimaging and switchable diffuser element. The proposed system is composed of a liquid crystal displayscreen, a lens array, a switchable diffuser element and a projector. The switchable diffuser element canbe controlled to present 2D/3D mixed image or 2D and 3D image independently, and it would reducethe Moire fringe and black grid. In addition to the improved display quality, the proposed system hasthe advantages of the simple structure and low cost, which contributes to the portability andpracticability.

Holography of particles for diagnostics tasks

Victor Dyomin, Alexander Gribenyukov, Alexandra Davydova, Michael Zinoviev, Alexey Olshukov, Sergey Podzivalov, Igor Polovcev, and Nikolay Yudin

Doc ID: 372786 Received 15 Jul 2019; Accepted 08 Oct 2019; Posted 08 Oct 2019  View: PDF

Abstract: The opportunities and special features of using a multi-purpose digital holographic camera (DHC) adapted for particle research for various diagnostic tasks, like plankton investigation in its habitat, optical glass diagnostics, and study of defects in single crystals, are investigated. Experimental research with the digital holographic camera carried out and described in this article have demonstrated universality of the DHC measurement technology and its effectiveness for solving a number of diagnostic tasks in the study of small particles of different natures in various media.

Atmospheric coherence time measurement by4-aperture DIMM defocus velocity technique

mohsen panahi, Ramin Shomali, mahmood mollabashi, and Saifollah Rasouli

Doc ID: 374072 Received 30 Jul 2019; Accepted 08 Oct 2019; Posted 08 Oct 2019  View: PDF

Abstract: In this work, we estimate the atmospheric Fried parameter r0, the average wind speed v and subsequentlythe atmospheric coherence time t0 by experimental measurement via a 4- aperture differential image motionmonitor (4-aperture DIMM) instrument at the Iranian National Observatory (INO) site. The experimentalapproach is based on the 4-aperture DIMM defocus velocity theory which uses the angle of arrival(AA) fluctuations measurement of a star light propagation through the atmospheric turbulence in formof a 4-spots configuration provided by the 4-aperture DIMM telescope. Here, we measure the defocusvariance s2C4 and its velocity variance s2¶C4/¶t and use the preceding theory to estimate the atmospheric turbulenceparameters. We have implemented the data sampling in INO site at an altitude of 3600 m abovethe sea level by a 12-inch Meade Cassegrain telescope consisting a 4-aperture mask at its entrance pupiland a fast CCD camera recording short-exposure images with frame rates in a range of 480 to 620 f ps fromthe Capella star. The experimental recorded data sets were analysed and the results were compared tothat of our simulation and other methods which demonstrated a good agreement.

Fabrication of a broadband anti-reflectionlayer using metal assisted chemical etching

fatemeh malekmohammad and mohammad malekmohammad

Doc ID: 373306 Received 22 Jul 2019; Accepted 07 Oct 2019; Posted 15 Oct 2019  View: PDF

Abstract: In this paper, an easy and cost-efficient method to create a single anti-reflectivelayer on a silicon substrate is presented. In this experiment, by using the silver nanoparticleson a silicon substrate at room temperature a porous nanostructure is created. Thisnanostructure significantly reduces the reflection and increases the transmission in a widespectral range. By using this method, a porous layer on one side of silicon substrate isfabricated. The results show that the reflection reduces to 31% and the transmission increasesto 68% in the 3500-5000 nm spectral range, which are close to the reflection and transmissionof a sample with ideal one-side anti-reflection.

Application of fiber-optic high repetition rate laser-ablationspark-induced breakdown spectroscopy on the elementalanalysis of aluminum alloys

Xiaoyong He, Runhua Li, and Yuqi Chen

Doc ID: 372684 Received 15 Jul 2019; Accepted 06 Oct 2019; Posted 07 Oct 2019  View: PDF

Abstract: Fiber-optic high repetition rate laser-ablation spark-induced breakdown spectroscopy was applied torealize elemental analysis of aluminum alloys. A compact fiber laser was used as source of laser-ablation andspark discharge was used to enhance the atomic emission of laser-induced plasma. Plasma emission spectrawere recorded with a compact fiber spectrometer in non-gated signal recording mode. Calibration curves of Cr,Cu, Mn, Mg and Zn in aluminum alloys were build under appropriate experimental condition and the detectionlimits of these elements were determined to be 4.4, 5.6, 4.9, 8.3 and 31.1 ppm, respectively. In comparisonwith those obtained in fiber-optic high repetition rate laser-induced breakdown spectroscopy using the samefiber laser, 3-18 improvement factor on the detection limit has been demonstrated. This system is compact andcost effective and the technique can be applied on rapid and convenient element analysis for different alloysamples.

Holographic response characteristicsinfluenced by absorptive diffusionpolymerization model in bulk TI/PMMAs

Peng Liu, Xiudong Sun, and Linlin Wang

Doc ID: 374495 Received 02 Aug 2019; Accepted 06 Oct 2019; Posted 07 Oct 2019  View: PDF

Abstract: Dynamic formation of volume holographic grating is mainly caused by thediffusion polymerization of photo-initiator in TI/PMMAs. Here, we consider the timedependentabsorption coefficient in this material to establish an absorption modulateddiffusion polymerization model. An experimental and theoretical investigation in TI/PMMAswith different sample thickness (1-3 mm) is presented. It is indicated that the thickness canregulate the holographic sensitivity and constancy in TI/PMMAs. Furthermore, we alsoexamined the dark diffusion process, multiplexed gratings recording, pre-exposureholographic enhancement and long-term full exposure in TI/PMMAs with different thicknessto analyze their holographic sensitivity and constancy. It is predicted that, in general, theabsorption characteristics in TI/PMMA can be further affected by changing its thickness, thusit is able to satisfy different requirements in high density holographic memories.

A three-wavelength polarization Scheimpfluglidar system developed for remote sensing ofatmospheric aerosols

Zheng Kong, Teng Ma, Ke Chen, Zhenfeng Gong, and Liang Mei

Doc ID: 375661 Received 16 Aug 2019; Accepted 05 Oct 2019; Posted 07 Oct 2019  View: PDF

Abstract: Multiple-wavelength polarization lidar techniques have been of great interest forthe studies of aerosol backscattering color ratio, Ångström exponent, particle size distribution,hygroscopic growth, etc. Conventional lidar techniques are mainly based on the time-of-flightprinciple. In this paper, a three-wavelength polarization Scheimpflug lidar (SLidar) system,based on the Scheimpflug imaging principle, has been developed for studying opticalproperties of atmospheric aerosols. The SLidar system utilizes low-cost, compact, multimodelaser diodes as light sources and two Complementary Metal Oxide Semiconductor (CMOS)sensors as detectors. The depolarization ratio was measured at the 808-nm band bysuccessively detecting atmospheric backscattering signals from two orthogonally polarizedlaser beam with a polarization CMOS camera, while the 520-nm and the 405-nmbackscattering signals were recorded by a second CMOS camera based on the timemultiplexingscheme. Atmospheric remote measurements have been carried out in May andJuly 2019 on a near horizontal path. The aerosol extinction coefficient, linear volumedepolarization ratio (LVDR) and the Ångström exponent have been retrieved and evaluated tostudy aerosol properties during different atmospheric conditions, which were in goodagreement with optical properties reported by previous studies.

Marine picoplankton size distribution andoptical property contrasts throughout theAtlantic Ocean revealed using flow cytometry

Timothy Smyth, Glen Tarran, and Shubha Sathyendranath

Doc ID: 370578 Received 24 Jun 2019; Accepted 05 Oct 2019; Posted 09 Oct 2019  View: PDF

Abstract: Depth-resolved flow cytometric (FC) observations have been used to determine thesize distribution and refractive index (RI) of picoplankton throughout the Atlantic Ocean.Prochlorococcus frequently showed double size distribution peaks centred on 0.75±0.25 and1.75±0.25 μm; smallest peak diameters were ≤0.65 μm in the equatorial upwelling with largercells (~0.95 μm) in the surface layers of the tropical gyres. Synechococcus was stronglymono-dispersed: smallest (~1.5 μm) and largest cells (~2.25 – 2.50 μm) being encountered inthe lowest and highest abundance regions respectively. Typical RI for Prochlorococcus wasfound to be ~1.06 whereas for Synechococcus surface RI varied between 1.04 – 1.08 at high –low abundances respectively.

Design of narrow-bandwidth refractive indexsensor based on cascaded few-mode longperiodfiber grating

Wenyu Wu, Zhengtian Gu, qiang ling, and Wenbin Feng

Doc ID: 372144 Received 10 Jul 2019; Accepted 04 Oct 2019; Posted 07 Oct 2019  View: PDF

Abstract: This work presents a novel design of cascaded few-mode long-period fiber grating(FM-CLPFG) refractive index sensor with narrow bandwidth, which is based on the feature ofnarrow-bandwidth loss peak of few-mode long-period fiber grating (FM-LPFG), and furtherreduce the loss peak bandwidth of a single FM-LPFG by cascading. On the basis of thecoupled-mode theory of FM-LPFG, the mutual interference between the loss peaks of eachmode is reduced and the loss peak coupling intensity is ensured by selecting the appropriategrating period and grating length. Furthermore, the influence of the cascaded fiber length andthe number of cascaded grating segments on the loss peak bandwidth are analyzed. Based onthe above designed parameters, the FM-CLPFG narrow-bandwidth sensor with a bandwidthof about 1 nm is designed. The results show that the sensitivity of this sensor is available to2410nm/RIU with the surrounding refractive index changing from 1.4445 to 1.4475.

Active Loss Compensation in the ResonantOptical Gyroscope with a ‘Reflector’: Towards aCost Effective Alternative for the NavigationalGrade.

SUMUKH NANDAN RAGHUNANDAN, Gowrishankar Ramadurai, and Shailesh Srivastava

Doc ID: 375141 Received 13 Aug 2019; Accepted 03 Oct 2019; Posted 03 Oct 2019  View: PDF

Abstract: The performance of passive fiber optic gyroscopes involving ring resonators are mainlylimited by loss and finesse of the cavity. In this work we show performance enhancement of therecently studied resonant fiber optic gyroscope with a ‘reflector’ using active loss compensation.Our gyroscope does not require expensive ultra-narrow linewidth lasers, expensive lock-indetection methods and polarization maintaining fibers which are mandatory for all standardresonant fiber optic gyroscopes. The performance of this gyroscope shows four-fold enhancementin the Q factor ¹2:2108º, compared to the earlier experimental setup involving losses. Enhancedsensitivity to rotation is experimentally demonstrated using loss compensation as well as tuningthe embedded reflector in the resonator. A shot noise limited sensitivity of 0.03 deg/h is possiblewith this experimental realization. This work demonstrates that our gyroscope can provide a costeffective alternative even in the navigational grade.

Gaussian beam with high spherical aberration focusedby a singlet lens-shaped container for glucosemeasurements

Etna Yáñez, Moisés Cywiak, juan franco, and David Cywiak

Doc ID: 371682 Received 04 Jul 2019; Accepted 03 Oct 2019; Posted 04 Oct 2019  View: PDF

Abstract: We describe a highly sensitive optical technique for glucose concentration measurements in liquid samples basedon measuring the heights of the primary side-lobes of the normalized intensity profiles of a focused Gaussian beamwith high spherical aberration. A singlet lens-shaped container, filled with the sample under test, is used to focusthe beam at an observation plane placed close to the focusing region. The normalized intensity profile of theaberrated beam allows for accurate measurement of the sample glucose concentration.

Autostereoscopic transparent display using a wedgelight guide and a holographic optical element:implementation and results

Thomas Crespel, Patrick Reuter, Adrian Travis, Yves Gentet, and Xavier Granier

Doc ID: 372798 Received 16 Jul 2019; Accepted 03 Oct 2019; Posted 04 Oct 2019  View: PDF

Abstract: We present a novel transparent autostereoscopic display consisting of laser picoprojectors, a wedge light guide, and a holographic optical element. The holographic optical element is optically recorded, and we present the recording setup, our prototype, as well as the results.Such a display can superimpose 3D data on the real world without any wearable.

Weak Measurement-Based Sensor for the RapidIdentification of L(+)-Ascorbic Acid and D(-)-Isoascorbic Acid

suyi zhong, Tian Guan, Yang Xu, Zhou Chongqi, Lixuan Shi, Cuixia Guo, Xuesi Zhou, Zhangyan Li, Yonghong He, and Yanhong Ji

Doc ID: 371972 Received 05 Jul 2019; Accepted 02 Oct 2019; Posted 04 Oct 2019  View: PDF

Abstract: The ability to identify L(+)-ascorbic acid from D(-)-isoascorbic acid in medicinal products is of practical interest.Based on the method of frequency domain weak measurement, a set of common optical path sensor foridentification of L(+)-ascorbic acid and D(-)-isoascorbic acid is established. By quantificationally analyzing themagnitude and offset direction of the spectral central wavelength, a good identification of the concentration andthe optically active forms of ascorbic acid has been achieved. The sensitivity and resolution of the sensor for opticalrotation can reach 34.35 nm/° and 5.53×10-5°, respectively. The detection resolution for L(+)-ascorbic acid is2.00×10-4 mol/mL, and that for D(-)-isoascorbic acid is 2.73×10-4 mol/mL. The potential of the sensor in thedetection of transparent but optically inactive impurities has been verified by comparative experiments of sodiumchloride solution. The sensor also has been applied to identify medicinal vitamin C tablets, which verified thefeasibility of the method in optically active pharmaceutical solutions with water-insoluble, optically inactiveimpurities. Since the sensor has the advantages of high precision, real-time, high robustness and non-destructive. Ithas a great prospect in the field of drug detection containing chiral molecules.

Light trapping schemes for silicon thin-filmsolar cells via super-quadratic subwavelengthgratings

Ke Chen, Rui Wu, Hongmei Zheng, Haishuo Wang, Guojun Zhang, and Shunhua Chen

Doc ID: 372197 Received 09 Jul 2019; Accepted 01 Oct 2019; Posted 02 Oct 2019  View: PDF

Abstract: We systematically investigate the light-trapping schemes of crystalline silicon thinfilmsolar cells (TFSCs) for three common grating layouts via one-dimensional superquadraticsubwavelength gratings (1D SQSWGs). The effects of antireflective coating,absorber layer thickness, and grating geometry on the light-trapping performance of TFSCsare numerically studied using the finite-difference time-domain method. The results suggestthat the conformal AZO coatings have better optical properties than the plane AZO coatings;for the case of only top Si gratings, the grating geometry of degree n = 4 can achieve a goodtradeoff between the shape-dependent light-trapping and antireflection properties, showingthe best light-trapping effect; for the case of only bottom Ag gratings, the optical performanceof TFSCs is significantly degraded as the degree n increases from n = 1 to n→∞. The abovefindings are analyzed and demonstrated in detail from the optical and electrical perspectives,and they can be utilized to guide the design of light-trapping structures for TFSCs.

Diffraction by ruled gratings with variablespacing: Fundamental method of intensitycalculation

S. Chatterjee, V. C. Vani, Rezvan Haghighi, and Ravinder Banyal

Doc ID: 366668 Received 02 May 2019; Accepted 01 Oct 2019; Posted 01 Oct 2019  View: PDF

Abstract: Regular diffraction grating produces intensity patterns that combines waves comingthrough equispaced slits, so that waves emerging from any two neighbouring slits have identicalphase difference. In the present communication we calculate the degradation in the intensitypattern when the grating has irregular spacings. The model of randomness considers the gratingspacings and openings being created by a ‘random walk’. The resolving power of the gratingis evaluated in relation to the D-lines of Sodium. It is shown, as number of rulings increases,uniformity of their spacing becomes more important in precision spectroscopic measurements asin astrophysical spectroscopy.

A Self-calibration Approach to Stereo Cameras withRadial Distortion Based on Epipolar Constraint

Guan Banglei, Yingjian Yu, Ang Su, Yang Shang, and Qifeng Yu

Doc ID: 373955 Received 08 Aug 2019; Accepted 01 Oct 2019; Posted 01 Oct 2019  View: PDF

Abstract: In this paper we propose a self-calibration approach to stereo cameras with radial distortion from stereoimage pairs of a common 3D scene. Based on the epipolar constraint existed in the stereo image pair, theintrinsic and extrinsic parameters of stereo cameras are estimated synchronously with a minimum numberof nine image point correspondences. It is significant within a random sample consensus (RANSAC)scheme, to cope with the outliers of feature matches efficiently and robustly. Then the inliers of stereoimage pair which have been determined after RANSAC are used to optimize the calibration parameters ofstereo cameras. Furthermore, more accurate calibration results can be achieved with the joint optimizationof multiple stereo image pairs. Both synthetic and real data are used to evaluate the performance of theproposed method, demonstrating that our method can calibrate stereo cameras with radial distortionsefficiently and accurately.

Finite Element Analysis of Fiber-Optic Fabry–PérotPressure Sensors based on Silicon Diaphragms

Rongkun Wang, Longfei Xiao, qi li, Xiangang Xu, Xiufang Chen, and Xuejian Xie

Doc ID: 374200 Received 31 Jul 2019; Accepted 30 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: Fiber-optic Fabry–Pérot pressure sensors based on silicon diaphragms of different thicknesses were fabricated usingsurface and bulk MEMS techniques in this study. The multi-beam interference resulting from multiple reflecting mirrorswith the elastic deformation of the Fabry–Pérot sensor was simulated by finite element analysis. The pressuresensitivities of the sensors with different diaphragm thicknesses and the relationship between the pressure and thewavelength shift were simulated. The simulation results were in good agreement with the test results. This studyprovides guidance for future sensor models and parameter design.

Two-component gas QEPAS sensor based onTime Division Multiplexing of DFB laser drivercurrent

zongliang wang, Jun Chang, Cunwei Tian, Yiwen Feng, Cheng Wang, Hao Zhang, Qinduan Zhang, Hefu Li, Zhenbao Feng, Xiukun Zhang, and Longfei Tang

Doc ID: 374559 Received 05 Aug 2019; Accepted 30 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: Two-component gas sensor in quartz enhanced photoacoustic spectroscopy(QEPAS) based on time-division multiplexing (TDM) technology of DFB laser driver currentwas proposed and experimentally demonstrated. The quartz tuning fork-based photoacousticspectroscopy (PAS) cell configuration with two optical collimators and two acousticmicroresonators was designed to detect the second harmonics (2f) PAS signal. The twooptical collimators guaranteed the two laser beams to inject the PAS cell conveniently,providing higher power input than 3 dB optical fiber coupler. Two-component gas sensingwas achieved by the TDM of DFB laser driver current. We used this two-component gassensing technique to detect acetylene (C2H2) at 1532.83 nm and methane (CH4) at 1653.722nm. The C2H2 and CH4 detection was achieved at 2.4 s interval. The minimum detectionlimits of 1ppmv for C2H2, and 13.14 ppmv for CH4 were obtained, and the linear responseswere reached 0.99968, 0.99652 for C2H2 and CH4 respectively. Moreover, the continuousmonitoring of CH4 and C2H2 for 40 min showed a good stability. The TDM technology ofDFB laser driver current would play an important role on the multi-component detection.

Simultaneous 3D measurement of deformationand its first derivative with speckle patterninterferometry and shearography

Qihan Zhao, Weijie Chen, Fangyuan Sun, Peizheng Yan, Bing Ye, and Yonghong Wang

Doc ID: 372340 Received 11 Jul 2019; Accepted 30 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: Digital speckle pattern interferometry and digital shearography are widely used innondestructive testing due to their advantages of high speed, full-field, and high sensitivity.However, traditional speckle pattern interferometry and shearography can only measure asingle variable of deformation or strain. This study presents a modified commonmeasurement setup that can simultaneously measure deformation and its first derivative. Inthe optical setup, a reference beam is introduced behind the shearing device to interfere withthe object beams, thereby simplifying the spectrum and improving the quality of the phasemaps. Then the spatial carrier technology is used to extract phase and achieve dynamicmeasurements. The proposed system also expands the measurement range using a 4f system.This study also presents a 3D optical setup based on the 1D system, which is more suitablefor practical measurement applications in industrial areas. Theoretical derivation andexperimental results are described and presented.

Freeform geometrical optics I: Principles

Juan Valencia-Estrada and Jorge Garcia-Marquez

Doc ID: 372408 Received 12 Jul 2019; Accepted 30 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: Lens design uses a calculation of the lens’ surfaces that permit to obtain an imagefrom a given object. A set of general rules and laws permits to calculate the essential pointsof the optical system such as distances, thickness, pupils, and focal distance among others.Now, the theory on which the classical lens design is based changes radically as ourtheoretical foundations do not rely on the classical ray tracing rules. We show that with therules expressed in a reduced vector analytical solution set of equations, we can take intoaccount all optical elements, i.e. refractive, reflective, catadioptric. These foundationspermit to keep under control the system aberration budget in every surface. It reduces thecomputation time dramatically. The examples presented here were possible because of theversatility of this theoretical approach.

White LED light source radar system for multiwavelengthremote sensing measurement ofatmospheric aerosols

Wenting Zhong, Jun Liu, hua Dengxin, Sasa Guo, Kejun Yan, and Chen Zhang

Doc ID: 369856 Received 26 Jun 2019; Accepted 30 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: A Mie scattering radar system with a white LED (light emitting diode) light source is proposed for themulti-wavelength detection of atmospheric aerosols. By splitting the continuous spectrum, the multi-wavelengthecho signals are extracted to achieve multi-wavelength real-time detection of atmospheric aerosols. The white LEDspectrum characteristics are analyzed, and four detection wavelengths are set at 450 nm, 525 nm, 600 nm and 661nm. The composition and detection principles of a white LED light source radar system are expounded, the designof each system part is described in detail, and the system parameters and data inversion algorithm are presented.We built a white LED light source radar system and conducted preliminary observation experiments. The resultsshow that radar can achieve multi-wavelength real-time detection of atmospheric aerosols within a 300 m height,which can provide effective data for further study of aerosol particle distribution and lay a foundation for furtherstudies of aerosol characteristics at special wavelengths.

Resolution and Contrast in Terahertz Pulse TimeDomain Holographic Reconstruction

Artem Turov, Maksim Kulya, Nikolai Petrov, and Andrei Gorodetsky

Doc ID: 372803 Received 17 Jul 2019; Accepted 30 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: Here, we present a comprehensive study of the reconstruction quality in terahertz (THz) pulse time domainholography. We look into single wavelength reconstructions, as well as broadband recovery enabledby ultrabroadband nature of radiation and coherent detection enabled by electro-optic or photoconductivesensing. We demonstrate the transverse resolution dependence for amplitude and phase objects onthe solid angle of the inline recorded time-domain THz hologram, and then turn to the contrast of reconstructedbinary amplitude objects, and further to longitudinal resolution of phase objects. We show thattransverse resolution can reach values comparable with the wavelength of the radiation used, and longitudinally,phase objects can be resolved with even greater precision. We compare the obtained resolutionwith theoretical estimates and show that THz pulse time domain holography is a powerful non-contactimaging tool.

Diffraction properties and applications of thespatially-structured optical fields with fractalamplitude masks

Yue Pan, Xu-Zhen Gao, Xu Zhang, Jia-Hao Zhao, Peng-Cheng Zhao, Yongnan Li, Chenghou Tu, and Hui-Tian Wang

Doc ID: 372948 Received 17 Jul 2019; Accepted 30 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: With fractal amplitude masks of Sierpinski carpet and Sierpinski triangle, wetheoretically and experimentally present the diffraction properties and applications of thespatially-structured optical fields including vector optical field, vortex optical field and vortexvector optical field. The diffraction patterns of the vector optical fields exhibit self-similarity,and the characteristics of the vector optical fields are maintained in every diffraction peak. Thediffraction patterns of the vortex optical fields and vortex vector optical fields exhibit triangularlattice arrays, and the vortex topological charge can be determined by the number of peak spotsin the triangular lattice array. We hope these diffraction properties with the fractal amplitudemasks can not only be applied in detecting topological charges of the spatially-structured opticalfields, but also in generating flexibly controlled diffraction patterns and lattice arrays which maybe useful in optical machining, optical trapping and information transmission.

Study on monitoring of optical emissions inlaser cladding of 316L stainless steel

peng yang, Gui Fang Sun, Yi Lu, and Zhonghua Ni

Doc ID: 373001 Received 17 Jul 2019; Accepted 30 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: Laser cladding is so complicated that some small disturbances may cause defects.Developing on-line monitoring technology for laser cladding is priority tasks. Compared withexpensive spectrometers and high speed cameras, an economical optical sensing system basedon two different photodiodes was established to optimize the laser parameter and helpmonitor the abnormal working condition. In order to find the optimal parameter, a series ofexperiments were carried out under different operating parameters such as laser power,scanning speed, and powder feeding rate. A practical rule is summarized to optimize processparameters by analyzing the time domain characteristics of the optical signal. Severalexperiments under different working conditions were performed to detect the abnormalworking condition. Not only can the abnormal situation be recognized, but also its type can bedistinguished by analyzing the optical signal in time and frequency domain. The opticalsensing system provides a better understanding and accurate evaluation of laser cladding.

Generation of Y-junction Bessel beams

Mathieu Fortin, Michel Piche, Denis Brousseau, and Simon Thibault

Doc ID: 373855 Received 08 Aug 2019; Accepted 29 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: A method is proposed to split the central spot of zero-order Bessel beams into two parallel spots along their propagation axis. The generation of these so-called Y-junction Bessel beams involves using an axicon and an optical component with a phase step profile. We show that this type of profile can be generated using a magnetic-liquid deformable mirror. Experimental results show a clear agreement with theoretical predictions. Potential applications of Y-junction Bessel beams are discussed.

Transmission filter controlled by incident conditions insingle-layer waveguide grating structures

Lina Fan, Kehui Jia, and Junshan Ma

Doc ID: 374713 Received 07 Aug 2019; Accepted 29 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: The classical single-layer waveguide grating structure is often designed as a reflection filter under 0° azimuthalangle condition. A new method for achieving transmission filter by modulating incident conditions is proposedrather than adjusting structural parameters. A 90° azimuthal angle ensures single resonance peaks, and largeincident angles provide a low-transmittance background. When the proposed single-layer waveguide gratingstructure is irradiated with an incident light azimuthal angle of 90° and incident angle of 86°, numerical resultsshow that high transmission peak emerges at 1550 nm with linewidth Δλ = 7.2 nm. Moreover, the transmissionpeak has nearly 100% transmittance. These findings show that modulating the incident conditions is also aneffective means apart from optimizing the structural parameters. The classical reflection filter can be reversed intotransmission filter using this method.

48×48 Pixelated Addressable Full-color MicroDisplay based on Flip-Chip Micro LEDs

Yang Li, Jin Tao, Yongzhou Zhao, Jiaxian Wang, Jin Lv, Yu Qin, Jingqiu Liang, and Weibiao Wang

Doc ID: 375438 Received 15 Aug 2019; Accepted 29 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: This paper reports on the design and fabrication of a 48×48 full-color pixelatedaddressable light emitting diode on silicon (LEDoS) micro display. The metallization patternwas designed and fabricated on a silicon substrate, while red, green, and blue monochromaticmicro LEDs were integrated on the silicon substrate using transfer printing. The red, green,and blue micro LEDs are flip-chip structures in which red micro LEDs were fabricated usingsubstrate transfer, mesa etching, metal deposition, and chip dicing. The integration processdoes not require wire bonding, which reduces the full-color pixel size and increases theintegration speed. The LEDoS micro display can be addressed individually for each LEDpixel and display representative patterns.

Computational Ghost Imaging via Adaptive DeepDictionary Learning

Xiang Zhai, Zhengdong Cheng, Zhenyu Liang, Chen Chen, Yangdi Hu, and Yuan Wei

Doc ID: 372475 Received 15 Jul 2019; Accepted 28 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: Ghost imaging has gone through from quantum to classical pseudo-thermal to computational field over the last twodecades. As a kernel part in computational ghost imaging (CGI), reconstruction algorithm plays a decisive role inimaging quality and system practicality. In order to introduce more prior knowledge into the reconstructionalgorithm, exiting researches add image patch prior into CGI and improve the imaging efficiency. In this paper, thetotal variation minimization algorithm via adaptive deep dictionary learning (TVADDL) is proposed to update anadaptive deep dictionary through the CGI reconstruction process. The proposed algorithm framework is able tocapture more precise texture features with multi-layer architecture dictionary and adapt the learned dictionary bygradient descent on CGI reconstruction loss value. The results of simulation and experiment show that TVADDL canachieve higher PSNR than the algorithms without patch prior and the algorithms using shallow dictionary or nonadaptivedeep dictionary.

Review of THz coherent lensless imaging

Lorenzo Valzania, Yuchen Zhao, Lu Rong, Dayong Wang, Marc Georges, Erwin Hack, and Peter Zolliker

Doc ID: 373049 Received 22 Jul 2019; Accepted 28 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: Imaging with THz radiation has proved an important tool for both fundamental science and industrial use. Here we review a class of THz imaging implementations, named coherent lensless imaging, that reconstruct the coherent response of arbitrary samples with a minimized experimental setup only based on a coherent source and a camera. After discussing the appropriate sources and detectors to perform them, we detail the fundamental principles and implementations of THz digital holography and phase retrieval. Despite these techniques owe a lot to imaging with different wavelengths, innovative concepts are also being developed in the THz range and are ready to be applied in other spectral ranges. This makes our review useful for both the THz and imaging communities, and we hope it will foster their interaction.

Hippopedal intensity plots: drawingcomparisons between antenna and opticalpolarimetry

Muhammad Hamza Waseem, Faizan E Ilahi, and Muhammad Anwar

Doc ID: 373290 Received 22 Jul 2019; Accepted 27 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: We present a graphical method to determine the polarization state of light. Wereview polarization profiling techniques used for antenna systems and correlate them withan optical analog. The analogy is used to perform tabletop optical polarimetry experiments.The experiments require intensity measurements and generating hippopedal polar plots. Themeasured polarimetry results are found to agree well with the theoretical predictions. Wealso set up a cost-effective quantum version of the experiment and reformulate the problem asthat of quantum state measurement. These experiments can be incorporated in the teachinglaboratory for both classical optics and quantum optics courses, offering a purely quantitative,albeit graphic technique for polarization analysis. These techniques are already employed fordesign of microwave antennas; the optic analogy is, therefore, interesting and useful.

Heat coupling effect on photothermal detection witha moving Gaussian excitation beam

Jingtao Dong and Rong-sheng Lu

Doc ID: 372234 Received 09 Jul 2019; Accepted 27 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: The strong photothermal response is beneficial to the measurement of optical and thermal properties of opticalmaterials using the laser-induced thermal mirror method. A highly sensitive asymmetrical thermal mirror methodwas recently proposed by employing a moving Gaussian excitation beam [J. T. Dong, T. D. Zhang, Y. Z. Zhang, L. Yang,and R. S. Lu, Appl. Phys. Lett. 114, 131902, 2019]. However, the heat transfer across the interface between thethermodynamic system and the surroundings is ignored, which will lead to an error in the absolute measurementof the material properties. To address the problem, we present a theoretical and experimental study of heattransfer within the heated sample and out to the air coupling fluid in the photothermal detection with a Gaussianexcitation beam moving at a constant velocity. We analyze the dynamic temperature fields inside the sample and inthe surrounding air, and the phase shifts induced by the thermoelastic displacement of the sample (thermalmirror) and the refractive index gradient of air (thermal lens), as well as the diffracted intensity profiles of theprobe beam in the detection plane. The experiments are implemented under normal pressure and vacuum,respectively, for a fused silica glass-air heat coupling system to verify the theoretical model. The experimentalresults show that the thermal lens due to the heat coupling effect introduces a signal deviation approximately 4.2%of the total photothermal signal, which is close to the theoretical result of 5%.

Narrowband Angle Filter

William Southwell

Doc ID: 378010 Received 13 Sep 2019; Accepted 27 Sep 2019; Posted 09 Oct 2019  View: PDF

Abstract: Narrowband pass filters are generally poor as narrowband angle filters. A tilted narrowband pass filter, however, is an improved narrowband angle filter, but only for rays in one plane of incidence. It is shown that a combination of two tilted narrowband pass filters will select light from all narrow angle patches in an incident cone. Furthermore, a design is presented for a narrow angle filter for three wavelengths, enabling transmission of tristimulus color gamut images while rejecting out of band and off-angle sources.

Multi-octave mid-infrared supercontinuum and frequency comb generation in a suspended As2Se3 ridge waveguide

Zeli Li, Jinhui Yuan, Chao Mei, Feng Li, Xian Zhou, Binbin Yan, Qiang Wu, Kuiru Wang, Xinzhu Sang, Ke-ping Long, and Chongxiu Yu

Doc ID: 372093 Received 08 Jul 2019; Accepted 26 Sep 2019; Posted 30 Sep 2019  View: PDF

Abstract: In this paper, we numerically investigate the mid-infrared supercontinuum (SC) generation in a suspended As2Se3 ridge waveguide, which is designed with the two zero-dispersion wavelengths. Simulation results show that when the pump pulses at wavelength 3.3 µm with width of 100 fs and peak power of 900 W are launched into the anomalous dispersion region of the designed waveguide with a length of 0.87 mm, the SC can be generated in the wavelength range from 1.76 to 14.42 µm (more than 3 octaves), extending deep into the “fingerprint” region. The stability of the generated SC is confirmed by the first-order coherence. Moreover, we demonstrate the performance of the SC-based frequency comb by assuming a 50-pulses pump source at a repetition rate of 100 MHz.

Augmenting performance of MEMS cantilever based photonic crystal waveguide for switching applications

Saurabh Agarwal, Jitendra Kumar Mishra, and Vishnu Priye

Doc ID: 372213 Received 10 Jul 2019; Accepted 26 Sep 2019; Posted 30 Sep 2019  View: PDF

Abstract: In this paper, Micro-Electro-Mechanical-System (MEMS) based cantilever is integrated as a line defect on photonic crystal silicon slab for optical switching applications. The elliptical holes are etched in the photonic crystal waveguide that results wide transmission bandwidth of 56 nm in comparison to etched circular holes in the structure with a footprint of only 12.5 µm×8 µm. The device is optimized for variation in height, the lattice constant, and semi-major and minor axis in the optical range of S-C-L band. It is shown that the response rise-time of the device is 21 µsec with very high extinction ratio of 30.4 dB and low insertion loss of 0.32 dB.

Exact global motion compensation forholographic video compression

Raees Kizhakkumkara Muhamad, David Blinder, Athanasia Symeonidou, Tobias Birnbaum, Osamu Watanabe, Colas Schretter, and Peter Schelkens

Doc ID: 372845 Received 16 Jul 2019; Accepted 25 Sep 2019; Posted 25 Sep 2019  View: PDF

Abstract: Holographic video requires impractical bitrates for storage and transmissionwithout data compression. We introduce an end-to-end compression pipeline for compressingholographic sequences with known ground truth motion. The compression strategy employsa motion compensation algorithm based on the rotational transformation of angular spectrum.Residuals arising from the compensation step are represented using short-time Fourier transformsand quantized with uniform mid-rise quantizers whose bit depth is determined by a Lagrangianrate-distortion optimization criterion where the distortion metric is the mean squared error.Experiments uses computer generated holographic videos and we report Bjøntegaard delta peaksignal to noise ratio gains of around 20 dB when compared to traditional image/video codecs.

Optimal processing scheme for restoration of phasedata corrupted by strong decorrelation noise anddislocations

Hai-Ting Xia, Silvio Montresor, Rongxin Guo, junchang Li, and Pascal Picart

Doc ID: 372447 Received 12 Jul 2019; Accepted 25 Sep 2019; Posted 26 Sep 2019  View: PDF

Abstract: The presence of speckle noise and dislocations makes phase restoration potentially difficult in quantitative phaseimaging and metrology. Unfortunately, there is no appropriate approach to deal with phase data corrupted by bothhigh speckle noise and phase dislocations. Usually, processing schemes may deal with low-pass phase filtering,phase unwrapping, or phase inpainting. This paper discusses on the efficient processing to deal with noisy phasemaps corrupted with phase dislocations. Six processing schemes, combining four operations are evaluated. Theinvestigation is carried out by realistic numerical simulations in which strong decorrelation phase noise and phasedislocations are generated. As a result, the most robust and faster processing is established. The applicability of theoptimal scheme is demonstrated through deformation measurement in dental materials.

High power, high beam quality spectralbeam combination of six narrow linewidthfiber amplifiers with two transmissiondiffraction gratings

Ye Zheng, Zhanda Zhu, Xiaoxi Liu, Miao Yu, Siyuan Li, Lin Zhang, Qingle Ni, Junlong Wang, and Xuefeng Wang

Doc ID: 374698 Received 06 Aug 2019; Accepted 25 Sep 2019; Posted 26 Sep 2019  View: PDF

Abstract: We demonstrate 10 kW spectral beam combination of six narrow linewidth fiber amplifiers bytwo transmission gratings with a combining efficiency about 90%. The wavelengths of incidentbeams range from 1056 nm to 1088nm. Each fiber amplifier delivers 2 kW output power laserwith 0.25 nm root-mean-square(RMS)linewidth. A dual grating beam combining system isconstructed to combine the six beams into a 10kW level high power beam and control the beamquality factor M2<2 by dispersion compensation. To the best of our knowledge, this is the highestoutput power combined by transmission gratings, which verifies the feasibility of transmissiongrating under high power density laser radiation and provides an alternative approach for highpower beam combining.

Investigation of the effect of gold coating ofgold-coated fiber on distributed strainmeasurement by DPP-BOTDA

Pengbai Xu, Ou Xu, Xinyong Dong, Jun Yang, and Yuwen Qin

Doc ID: 375508 Received 16 Aug 2019; Accepted 25 Sep 2019; Posted 26 Sep 2019  View: PDF

Abstract: Gold-coated fiber (GCF) shows the potential to sense strain at high temperatureowe to the hermeticity of gold coating that prevents hydrogen penetration. Nevertheless, thereare trivial details of the gold coating of GCF that need to be addressed before using GCF tomeasure strain at high temperature. In this study, we thoroughly investigate the effect of thegold coating of GCF on strain measurement both at room temperature and high temperatureup to 700 °C with differential pulse pair Brillouin optical-time analysis (DPP-BOTDA).Owing to the inhomogeneity of gold coating induced by the manufacturing process, it isnecessary to select the GCF with the gold coating of better homogeneity via DPP-BOTDA.Due to the residual stress that solidified in the GCF during the cooling process of coating, theGCF would first undergo plastic deformation and then elastic deformation in the strainmeasurement. After one-time strain measurement to remove the residual stress of GCF, thestandard deviation of the strain coefficients at room temperature and high-temperature are ±0.5% and ±1.3%, respectively, which is mainly due to the non-uniform thickness of the goldcoating and the nonuniformity of silica fiber at high temperature.

2-D MoTe2 film as saturable absorber for wavelength-tunable ultrafast fiber laser

Xiaoxiang Han

Doc ID: 375709 Received 19 Aug 2019; Accepted 24 Sep 2019; Posted 26 Sep 2019  View: PDF

Abstract: We have demonstrated the realization of wavelength-tunable pulse outputs in a mode-locked fiber laser by utilizing 2-D MoTe2 film as the saturable absorber (SA). The SA is synthesized by coating 2-D MoTe2 film on the pinhole of fiber pigtail and it can work stably at mode-locking state for several weeks, indicating that the 2-D MoTe2 film is a suitable SA for ultrafast optics. The MoTe2 film mode-locked fiber laser can operate well at a wide spectral band, and the central wavelength of pulses is tunable in the range from 1530 to 1560 nm. Our new SA will benefit high-power pulsed laser, materials processing, and frequency comb spectroscopy.

Pattern Recognition algorithm and SoftwareDesign of Optical Fiber Vibration SignalBased on Φ-OTDR

TABI FOUDA BERNARD MARIE, Dezhi Han, and Bowen An

Doc ID: 375791 Received 19 Aug 2019; Accepted 24 Sep 2019; Posted 25 Sep 2019  View: PDF

Abstract: A phase-sensitive optical time-domain reflectometry (Φ-OTDR) with a detection distance of 10 km isused in this paper to recognize and to detect in real time events along the perimeter securitymonitoring system. To optimize the signal processing in the software system, and achieve the designof Distributed Optical Fiber Vibration Signal of the perimeter security monitoring system, a Two-Level Vibration Pattern Recognition Scheme based on the Power Spectral Estimation (PSE) isproposed. The monitoring system software of the proposed algorithm is designed and implemented;as well as the functional modules involved in the design of the software system. The experimentaltests of the whole system show that the proposed algorithm can effectively identify in real-time anyintrusion event along the sensing cable, with the intrusion detection rate greater than 95%, includingfalse alarm. Also, the corresponding monitoring system software can display the data collected in thereal-time, with a processing time of around 1.6s, which proves its reliability; thereby ensuring thesystem's validity.

Camera calibration using a planar target with pure translation

Yang Mao, Xiaobo Chen, and Chengyi Yu

Doc ID: 369107 Received 03 Jun 2019; Accepted 24 Sep 2019; Posted 26 Sep 2019  View: PDF

Abstract: This paper presents a novel camera calibration method using a planar target with pure translation and thetranslation distance need to be known. It only requires the straightness and position accuracy of the one-axistranslational platform. There is no constraint among the normal direction of the planar target, the optical axisdirection of the camera and the moving direction of the translational platform theoretically. The paper analysis theclosed-form solution, followed by a nonlinear refinement based on the maximum likelihood criterion. Bothcomputer simulation and real data are implemented to verify the effective of the proposed method. Compared withZhang’s method, the proposed method realizes the camera calibration process automatically and evaluates thecalibration process via the measurement accuracy of the calibrated camera, so it is a key factor to advance 3Dcomputer vision one more step from expert use to worker use.

A novel algorithm to derive inherent opticalproperties from remote sensing reflectance in turbidand eutrophic lakes

kun xue, Emmanuel Boss, Ronghua Ma, and Ming Shen

Doc ID: 375485 Received 15 Aug 2019; Accepted 23 Sep 2019; Posted 23 Sep 2019  View: PDF

Abstract: Inherent optical properties play an important role in understanding the biogeochemical processes of lakes byproviding proxies for a variety of biogeochemical quantities, including phytoplankton pigments. However, to date,it has been difficult to accurately derive the absorption coefficient of phytoplankton (aph(λ)) in turbid andeutrophic waters from remote sensing. A large dataset of remote sensing of reflectance (Rrs(λ)) and absorptioncoefficients were measured for samples collected from lakes in the middle and lower reaches of the Yangtze Riverand Huai River basin (MLYHR), China. In the process of scattering correction of spectrophotometric measurements,the particulate absorption coefficients (ap(λ)) were first assumed to have no absorption in the Near Infrared (NIR)wavelength. This assumption was corrected by estimating the particulate absorption coefficients at 750 nm(ap(750)) from the concentrations of chlorophyll-a (Chla) and suspended particulate matter (SPM), which wasadded to the ap(λ) as a baseline. The resulting mean spectral mass-specific absorption coefficient of the non-algalparticles (NAP) was consistent with previous work. A novel iterative IOP inversion model was then designed toretrieve the total non-water absorption coefficients (anw(λ)), backscattering coefficients of particulates (bbp(λ)),aph(λ), and adg(λ) (absorption coefficients of NAP and colored dissolved organic matter (CDOM)) from Rrs(λ) inturbid inland lakes. The proposed algorithm performed better than previously published models in deriving anw(λ)and bbp(λ) in this region. The proposed algorithm performed well in estimating the aph(λ) for wavelengths > 500 nmfor the calibration dataset (N=285, UAPD =55.22%, RMSE =0.44 m-1) and for the validation dataset (N=57, UAPD=56.17%, RMSE =0.71 m-1). This algorithm was then applied to Sentinel-3A OLCI (Ocean and Land ColourInstrument) satellite data, and was validated with field data. This study provides an example of how to use localdata to devise an algorithm to obtain IOPs, and in particular, aph(λ), using satellite Rrs(λ) data in turbid inlandwaters.

Tunable narrow terahertz absorption of onedimensionalphotonic crystals embedded withDirac semimetal-dielectric defect layers

Qin WANG and liwei Zhang

Doc ID: 370420 Received 24 Jun 2019; Accepted 23 Sep 2019; Posted 24 Sep 2019  View: PDF

Abstract: The absorption characteristics of one-dimensional photonic crystals embeddedwith Dirac semimetal-dielectric defect layers are studied using transfer matrix method.Numerical results show that our proposed structure can realize near perfect narrow absorptionfor its strong field localization effects. The absorption frequency is tunable by adjusting theFermi energy of the Dirac semimetal, temperature, permittivity of the dielectric and thestructural parameters. Moreover, double or multiple absorption channels can be achieved bychanging the structure. Furthermore, the absorption performance is wide-angel and insensitiveto polarization of the incident wave. Such properties exhibit potential value in designingselective absorbers and thermal detectors.

Surface Plasmon Resonance Biosensor Based onHexagonal Lattice Dual Core Photonic Crystal Fiber

Tanvir Ahmed, Alok Kumar Paul, Md. Shamim Anower, and S. M. Razzak

Doc ID: 373942 Received 06 Aug 2019; Accepted 23 Sep 2019; Posted 26 Sep 2019  View: PDF

Abstract: In this article, the guiding properties and sensor performance are numerically investigated for a dual corehexagonal lattice photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR). Gold is used as theactive plasmonic material in order to create resonance and placed outside the fiber structure to facilitate fabricationprocess. The finite element method (FEM) is used to numerically investigate the characteristics of the sensor. Bymeans of wavelength and amplitude interrogation methods, it is found that the proposed sensor shows maximumwavelength sensitivity of 16000 nm/RIU with 6.25×10-6 RIU resolution and amplitude sensitivity of 2255 RIU-1 with4.40×10-6 RIU resolution, respectively. The proposed SPR sensor can detect analyte refractive index ranging from1.33 to 1.40. This work also includes the investigation of the effect of change of gold layer thickness, air-hole diameterand analyte layer on the sensor performance from the optimized design. The proposed sensor could be employed todetect biological and biochemical analytes because of its simple design and promising results.

Focal plane array-based compressive imaging inmedium wave infrared: modelling, implementationand challenges

Zimu Wu and Xia Wang

Doc ID: 371556 Received 02 Jul 2019; Accepted 23 Sep 2019; Posted 23 Sep 2019  View: PDF

Abstract: As a super-resolution imaging method, compressive imaging (CI) is a research hotspot in recent years. However,most researches focus on the visible light and near-infrared regime. Most experimental studies are confined tosingle pixel camera, and there are comparatively few reports of the experimental studies about CI in the field offocal plane array-based (FPA) CI in medium wave infrared (MWIR). This paper derives the system model for FPA CIsystem, describes the generation process of DMD masks and modifies the block-based compressive sensing (BCS)algorithm to be applicable to FPA CI system. Based on the actual FPA CI system in MWIR, high-resolution MWIRimages are obtained from a low-resolution MWIR sensor, realizing 16 times MWIR image super-resolution.However, imaging quality is not as cheerful as that in visible light FPA CI system, because of the particularities ofMWIR. We analyze the particularities of FPA CI system in MWIR, and provide some suggestions on how to solvethem to improve performance. This work could provide guidance for researchers to build experimental FPA CIsystem in MWIR.

The Injection Laser System for AdvancedRadiographic Capability using Chirped PulseAmplification on the National Ignition Facility

John Heebner, David Alessi, Robert Acree, Adrian Barnes, Mark Bowers, Donald Browning, Tracy Budge, Scott Burns, Leyen Chang, Kim Christensen, John Crane, Michael Dailey, Gaylen Erbert, Matthew Fischer, Michael Flegel, Brad Golick, John Halpin, Mathew Hamamoto, Mark Hermann, Vincent Hernandez, John Honig, Jeffrey Jarboe, Daniel Kalantar, Vernon Kanz, Kenn Knittel, Jeremy Lusk, William Molander, Valier Pacheu, Mitanu Paul, Lawrence Pelz, Matthew Prantil, Michael Rushford, nick schenkel, Ronald Sigurdsson, Thomas Spinka, Michael Taranowski, Paul Wegner, k wilhelmsen, J. Nan Wong, and Steven Yang

Doc ID: 373841 Received 02 Aug 2019; Accepted 23 Sep 2019; Posted 23 Sep 2019  View: PDF

Abstract: We report on the design, performance, and qualification of the Injection LaserSystem (ILS) designed to deliver Joule-level chirped pulse beamlets arranged in dualrectangular beam formats into two main laser amplifier beamlines of the National IgnitionFacility (NIF). The system is designed to meet the requirements of the AdvancedRadiographic Capability (ARC) upgrade with features that deliver performance, adjustability,and long-term reliability.

Six-direction pseudo-random consecutive unicursalpolishing path for suppressing mid-spatial frequencyerror and realizing consecutive uniform coverage

Qizhi Zhao, Lei Zhang, and Cheng Fan

Doc ID: 374359 Received 01 Aug 2019; Accepted 22 Sep 2019; Posted 23 Sep 2019  View: PDF

Abstract: Planning of the polishing path is an important part for polishing process. Reasonable selection of the polishing pathcan improve surface quality and reduce the mid-spatial frequency (MSF) error. In this paper, a six-directionpseudo-random consecutive unicursal polishing path and the corresponding generation method are proposed. Theproposed path is especially useful for suppressing the MSF error of the surface and realizing consecutive uniformcoverage. Compared with traditional polishing paths such as scanning path, spiral path and fractal path, theproposed path has following characteristics: multi-directionality, high randomness, smoothness andconsecutiveness. In order to verify that the proposed path has the ability to suppress the MSF error, a group ofcontrast experiments were conducted and the measurement data was processed by the Empirical ModeDecomposition (EMD) method and the Fast Fourier Transform (FFT) method. The results show that the fluctuationamplitude of the MSF error and the fluctuation area with MSF error are reduced obviously by using the proposedpath. Besides, the corresponding wavelength of the crests in the spectrum shows multi-values. The experimentalresults show the proposed path has high randomness and the ability to suppress the MSF error.

Sparse aperture arrangement for periodic LEDarray sampling in FPM system

Haobo cheng, Xin Chen, yongfu wen, Huaying Wang, and hui li

Doc ID: 374459 Received 01 Aug 2019; Accepted 22 Sep 2019; Posted 23 Sep 2019  View: PDF

Abstract: In a traditional Fourier ptychography microscopy (FPM) system, multiple lowresolution(LR) intensity images have to be sequentially captured under variable illuminationangles and then stitched together in the Fourier domain, which is time-consuming. This paperproposes a sparse aperture arrangement method, in which the relationship between the spatialspectrum distribution and the light-emitting diodes array sampling pattern is investigated.Mathematical models of the proposed method are developed, and numerical simulations andoptical experiments are demonstrated to verify its feasibility. The results show that the numberof LR images could be decreased significantly without sacrificing image reconstructionquality. To the best of our knowledge, this is the first time that the sparse aperturearrangement has been exploited for FPM. The proposed method may provide new insights forimproving the efficiency of the FPM platform and discovering more applications in digitalpathology.

Measurement of internal stray radiation of athermal infrared spectrometer based on temperaturevariation

Peng Jun, Yue Xu, Hao-Ting Du, Zi-Hao Ying, Meng-Yang Chai, De-Xin Sun, and liu n

Doc ID: 369286 Received 05 Jun 2019; Accepted 22 Sep 2019; Posted 23 Sep 2019  View: PDF

Abstract: The level of internal stray radiation is an important criterion to evaluate the performance of a thermalinfrared spectrometer. In this study, a novel method is proposed and evaluated to measure the internal strayradiation of a thermal infrared spectrometer based on temperature variation. The proposed method wasused to measure the internal stray radiation values of an existing instrument. Firstly, two output gray valuecurves were constructed for a single spectral channel in a cryogenic detector at two different spectrometertemperatures based on radiometric calibration measurements. Subsequently, the gray value and radiationflux of the internal stray radiation of the spectrometer were calculated. In addition, the internal strayradiation data measured at different spectral channels and different integration time were used to verify andevaluate the proposed method. Results show that the proposed method is valid, and the standard deviationsof the various internal radiation values of the tested spectral channels and the various integration time are3.47% and 1.46%, respectively. The proposed method is adaptable, flexible, and efficient.

Improvements of Phase Linearity and Phase Flicker ofPhase-Only LCoS Devices for Holographic Applications

Yuan Tong, Mike Pivnenko, and Daping Chu

Doc ID: 372719 Received 15 Jul 2019; Accepted 20 Sep 2019; Posted 23 Sep 2019  View: PDF

Abstract: Significant phase distortion corrections were achieved by optimizing the digital driving patterns of phase-onlyLCoS devices for digital holographic applications. Nearly perfect phase linearity and phase flicker of 0.09% over256 addressed phase levels in respect to the total modulation range of 2π were realized, enabling a meaningfulincrease of phase levels from 8 bits (256 levels) to 9 bits (512 levels). Tests were carried out to evaluate thequalities of optically reconstructed holographic images with reduced phase flicker and optimised phase linearity,and an increase of 17.7% in the RMS contrast was demonstrated.

3D object recognition through processing of2D holograms

Behzad Bordbar, Haowen Zhou, and Partha Banerjee

Doc ID: 372855 Received 16 Jul 2019; Accepted 20 Sep 2019; Posted 23 Sep 2019  View: PDF

Abstract: Correlation of two-dimensional digitally recorded holograms is introduced as anovel approach for object recognition without the need for quantitative assessment of theretrieved complex field, based on the fact that a hologram contains the three-dimensionalinformation of the object. Actual objects with different three-dimensional features such asdepth and surface roughness are assessed through processing of the correlation of their twodimensionalholograms. Correlation peak values are extracted as a metric to evaluatecorrelation of three-dimensional objects. The effect of hologram windowing size oncorrelation of three-dimensional objects are investigated and improvements in computationtime and dynamic range are assessed. Critical figures of merit used for assessment ofcorrelation of images are applied to the correlation of holograms for object recognition.

Joint 3D Localization and Classification of SpaceDebris using a Multispectral Rotating Point SpreadFunction

Chao Wang, Grey Ballard, Robert Plemmons, and Sudhakar Prasad

Doc ID: 369872 Received 12 Jun 2019; Accepted 20 Sep 2019; Posted 20 Sep 2019  View: PDF

Abstract: We consider the problem of joint three-dimensional (3D) localization and material classification of unresolvedspace debris using a multispectral rotating point spread function (RPSF). The use of RPSF allowsone to estimate the 3D locations of point sources from their rotated images acquired by a single 2D sensorarray, since the amount of rotation of each source image about its x, y location depends on its axial distancez. Using multi-spectral images, with one RPSF per spectral band, we are able not only to localizethe 3D positions of the space debris but also classify their material composition. We propose a three-stagemethod for achieving joint localization and classification. In Stage 1, we adopt an optimization schemefor localization in which the spectral signature of each material is assumed to be uniform, which significantlyimproves efficiency and yields better localization results than possible with a single spectral band.In Stage 2, we estimate the spectral signature and refine the localization result via an alternating approach.We process classification in the final stage. Both Poisson noise and Gaussian noise models are considered,and the implementation of each is discussed. Numerical tests using multispectral data from NASA showthe efficiency of our three-stage approach and illustrate the improvement of point source localization andspectral classification from using multiple bands over a single band.

Identification of heavy metal by testingmicroalgae using confocal Ramanmicrospectroscopy technology

Aiping Gong, Weiming Gu, Zhenyu Zhao, and Shao Yongni

Doc ID: 371369 Received 15 Jul 2019; Accepted 20 Sep 2019; Posted 24 Sep 2019  View: PDF

Abstract: Five copper concentrations (0, 0.5, 1, 2, 4mg/L) were used to stress C. pyrenoidosafor continuously 5 days. The biomass, chlorophyll and carotenoids of microalgae weremeasured, and Raman mapping spectral and Raman single-point spectral of microalgae wasacquired. Principal component-linear discriminant analysis (PC-LDA), back propagationartificialneural network (BP-ANN) and sensitive wavelengths-linear discriminant analysis(SW-LDA) were used to build models to identify different copper concentrations using thespectral data after pretreatment. The results showed that BP-ANN model was the optimal toidentify copper concentrations with prediction accuracy of 92% in day4

The Hanle effect in laser-induced fluorescence and Naand Fe resonance scattering lidars

Chiao-Yao She

Doc ID: 373848 Received 26 Jul 2019; Accepted 18 Sep 2019; Posted 18 Sep 2019  View: PDF

Abstract: The nature of the Hanle effect on laser-induced fluorescence (LIF) remains subtle and physically ambiguous. Byassociating the Hanle effect to the linearly superposed phase-locked excited sub-states induced by laser-likecoherent light, this paper attempts to demystify its underline physics. The resulting LIF radiation leads to anangular distribution of radiation, whose detail depends on the quantum structure of the target atoms. Three simplequantum radiators are used to illustrate the fact that LIF could result in distributions ranging from that ofspontaneous emission to that of classical dipole oscillator. The radiation patterns of 6 Na D2 and 5 Fe transitions ofinterest are presented. The non-unity backward enhancement q factor of a transition alters its contributionproportionally to the received lidar signal, thus it results in temperature and wind errors if this factor is ignored indata processing of Na and Fe Doppler lidars, as well as of the Fe Boltzmann lidar; these errors are shown to be lessthan 1 K and 1 m/s.

Visualizing the prediction of the laser cleaning: a dynamic preview method with multi-scale conditional generative adversarial network

Zhang Hui, Zhao Jia, Sun Bo, and He Jun

Doc ID: 367016 Received 08 May 2019; Accepted 18 Sep 2019; Posted 19 Sep 2019  View: PDF

Abstract: As producing high power per unit area and obtaining immediate feedback, laser offers the potential for high-precision surface processing. However, due to consisting of many complex and nonlinear physiochemical processes, unfitted values of parameters can easily result in undesired cleaned results, the substrate is either damaged or not cleaned. Thus, an accurate, flexible and automatic image preview method is highly demanded in the cleaning practice. Here we propose a multi-scale conditional generative adversarial network (MS-CGAN), which allows workers to view what a cleaned version of the surface would look like before actually cleaning so that it can assist workers in adjusting laser parameters in advance to obtain desired cleaned results for resource saving and efficiency improvement. The advantage of this method is that it requires zero knowledge of the mechanism of laser, and hence avoids the need for modelling the complex photon–atom interactions that occur in laser cleaning. Extensive experiments showthat MS-CGAN not only can visualize the high fidelity prediction of laser cleaning effect but also produce the preview images that exactly match the cleaned surfaces. The method provides an option for industry benefits, such as minimizing the risk of wasting resource, sustaining the environment, and cutting the cost of labor.

Nonuniformity correction of polarization response for liquid crystal modulated polarimeter

zhang xin, Zhang Bao, Hong Feng, wu da, and fang xufang

Doc ID: 374753 Received 06 Aug 2019; Accepted 18 Sep 2019; Posted 09 Oct 2019  View: PDF

Abstract: Liquid crystal modulated polarimeters (LCMPs) are often used to detect the full polarization information of target scenes. In this study, a nonuniformity correction method based on reference source calibration for LCMP is proposed. We analyze the error sources of the polarimeter and establish a grayscale response model with nonuniformity noises. The gain and bias correction coefficient of each pixel are calculated based on the linear response property of the detector. The polarization parameters of each detection unit of the uniform light source with the same polarization state calculated by the corrected Stokes vector are uniform. Results show that the error of the degree of linear polarization is reduced by 5.08%, and the degree of circular polarization is reduced by 19%. Therefore, the proposed method effectively improves the nonuniformity and detection accuracy of polarimeters.

CHIMERA, a new holoprinter technology combininglow-power continuous lasers and fast printing

Yves Gentet and Philippe Gentet

Doc ID: 372858 Received 16 Jul 2019; Accepted 13 Sep 2019; Posted 13 Sep 2019  View: PDF

Abstract: This paper presents CHIMERA, the third generation of digital holographic printing system that solves the knownproblems of the two previous generations. This holoprinter is based on the use of low-power RGB continuouslasers combined with the ultra-fine grain silver-halide material Ultimate U04, and is capable of printing at afrequency equal or greater than 25 hogels per second, full-color, 120° full-parallax digital reflection holograms orholographic optical elements with a size of up to 60×80 cm and a hogel size ranging from 250 to 500 μm. A 3Dscanner using a 4K video camera has been specially designed for scanning real objects printable on Chimera.CHIMERA offers new achievements in term of color rendition, palette and accuracy, and opens new perspectives fordigital holography applications and holography in general.

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