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Simple and sensitive technique for alignment of the pinhole of a spatial filter of a high-energy, high-power laser system

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APPLIED OPTICS 2013年第12期52卷 2546-2554页

作者： Sharma, Avnish Kumar Patidar, Rajesh Kumar Daiya, Deepak Joshi, Anandverdhan Naik, Prasad Anant Gupta, Parshotam Dass Raja Ramanna Ctr Adv Technol Laser Plasma Div Indore 452013 Madhya Pradesh India

In this paper, a new method for alignment of the pinhole of a spatial filter (SF) has been proposed and demonstrated experimentally. The effect of the misalignment of the pinhole on the laser beam profiles has been calculated for circular and elliptical Gaussian laser beams. Theoretical computation has been carried out to illustrate the effect of an intensity mask, placed before the focusing lens of the SF, on the spatial beam profile after the pinhole of the SF. It is shown, both theoretically and experimentally, that a simple intensity mask, consisting of a black dot, can be used to visually align the pinhole with a high accuracy of 5% of the pinhole diameter. The accuracy may be further improved using a computer-based image processing algorithm. Finally, the proposed technique has been demonstrated to align a vacuum SF of a compact 40 J Nd:phosphate glass laser system. (C) 2013 Optical Society of America

关键词： image processing algorithms Laser beams Laser systems Optical amplifiers Optical parametric chirped pulse amplification Solid state lasers

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Accurate 3D tracking and size measurement of evaporating droplets using in-line digital holography and "inverse problems" reconstruction approach

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OPTICS EXPRESS 2013年第23期21卷 27964-27980页

作者： Seifi, Mozhdeh Fournier, Corinne Grosjean, Nathalie Mees, Loic Marie, Jean-Louis Denis, Loic Univ Lyon F-42023 St Etienne France Univ St Etienne Telecom St Etienne Lab Hubert Curien CNRSUMR5516 F-42000 St Etienne France Univ Lyon 1 INSA Lyon CNRS Lab Mecan Fluides & AcoustUMR5509Ecole Cent Lyo F-69134 Ecully France

Digital in-line holography was used to study a fast dynamic 3D phenomenon: the evaporation of free-falling diethyl ether droplets. We describe an unsupervised reconstruction algorithm based on an "inverse problems" approach previously developed by our team to accurately reconstruct 3D trajectories and to estimate the droplets' size in a field of view of 7 x 11 x 20 mm(3). A first experiment with non-evaporating droplets established that the radius estimates were accurate to better than 0.1 mu m. With evaporating droplets, the vapor around the droplet distorts the diffraction patterns in the holograms. We showed that areas with the strongest distortions can be discarded using an exclusion mask. We achieved radius estimates better than 0.5 mu m accuracy for evaporating droplets. Our estimates of the evaporation rate fell within the range predicted by theoretical models. (C) 2013 Optical Society of America

关键词： Digital holographic imaging image processing algorithms Inverse problems Ptychography Reconstruction algorithms Three dimensional imaging

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Analysis of cellular objects through diffraction images acquired by flow cytometry

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OPTICS EXPRESS 2013年第21期21卷 24819-24828页

作者： Zhang, Jun Feng, Yuanming Moran, Marina S. Lu, Jun Q. Yang, Li V. Sa, Yu Zhang, Ning Dong, Lixue Hu, Xin-Hua Tianjin Univ Dept Biomed Engn Tianjin 300072 Peoples R China Tianjin Med Univ Canc Inst & Hosp Dept Radiat Oncol Tianjin 300060 Peoples R China E Carolina Univ Dept Phys Greenville NC 27858 USA E Carolina Univ Brody Sch Med Dept Oncol Greenville NC 27834 USA

It was found that the diffraction images acquired along the side scattering directions with objects in a cell sample contain pattern variations at both the global and local scales. We show here that the global pattern variation is associated with the categorical size and morphological heterogeneity of the imaged objects. An automated image processing method has been developed to separate the acquired diffraction images into three types of global patterns. Combined with previously developed method for quantifying local texture pattern variations, the new method allows fully automated analysis of diffraction images for rapid and label-free classification of cells according to their 3D morphology. (C) 2013 Optical Society of America

关键词： Forward scattering image analysis image processing image processing algorithms Speckle patterns Systems design

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Shutterless solution for simultaneous focal plane array temperature estimation and nonuniformity correction in uncooled long-wave infrared camera

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APPLIED OPTICS 2013年第25期52卷 6266-6271页

作者： Cao, Yanpeng Tisse, Christel-Loic MTech Imaging Pte Ltd Singapore 499629 Singapore

In uncooled long-wave infrared (LWIR) microbolometer imaging systems, temperature fluctuations of the focal plane array (FPA) result in thermal drift and spatial nonuniformity. In this paper, we present a novel approach based on single-image processing to simultaneously estimate temperature variances of FPAs and compensate the resulting temperature-dependent nonuniformity. Through well-controlled thermal calibrations, empirical behavioral models are derived to characterize the relationship between the responses of microbolometer and FPA temperature variations. Then, under the assumption that strong dependency exists between spatially adjacent pixels, we estimate the optimal FPA temperature so as to minimize the global intensity variance across the entire thermal infrared image. We make use of the estimated FPA temperature to infer an appropriate nonuniformity correction (NUC) profile. The performance and robustness of the proposed temperature-adaptive NUC method are evaluated on realistic IR images obtained by a 640 x 512 pixels uncooled LWIR microbolometer imaging system operating in a significantly changed temperature environment. (C) 2013 Optical Society of America

关键词： image processing image processing algorithms image quality Imaging systems Motion estimation Thermal infrared imaging

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A real-time noise filtering strategy for photon counting 3D imaging lidar

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OPTICS EXPRESS 2013年第8期21卷 9247-9254页

作者： Zhang, Zijing Zhao, Yuan Zhang, Yong Wu, Long Su, Jianzhong Harbin Inst Technol Dept Phys Harbin 150001 Peoples R China Tianjin Jinhang Inst Technol Phys Tianjin 300192 Peoples R China

For a direct-detection 3D imaging lidar, the use of Geiger mode avalanche photodiode (Gm-APD) could greatly enhance the detection sensitivity of the lidar system since each range measurement requires a single detected photon. Furthermore, Gm-APD offers significant advantages in reducing the size, mass, power and complexity of the system. However the inevitable noise, including the background noise, the dark count noise and so on, remains a significant challenge to obtain a clear 3D image of the target of interest. This paper presents a smart strategy, which can filter out false alarms in the stage of acquisition of raw time of flight (TOF) data and obtain a clear 3D image in real time. As a result, a clear 3D image is taken from the experimental system despite the background noise of the sunny day. (C) 2013 Optical Society of America

关键词： Avalanche photodiodes Geiger modes image processing image processing algorithms Photon counting Three dimensional imaging

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Gradient-based interpolation method for division-of-focal-plane polarimeters

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OPTICS EXPRESS 2013年第1期21卷 1137-1151页

作者： Gao, Shengkui Gruev, Viktor Washington Univ Dept Comp Sci & Engn St Louis MO 63130 USA

Recent advancements in nanotechnology and nanofabrication have allowed for the emergence of the division-of-focal-plane (DoFP) polarization imaging sensors. These sensors capture polarization properties of the optical field at every imaging frame. However, the DoFP polarization imaging sensors suffer from large registration error as well as reduced spatial-resolution output. These drawbacks can be improved by applying proper image interpolation methods for the reconstruction of the polarization results. In this paper, we present a new gradient-based interpolation method for DoFP polarimeters. The performance of the proposed interpolation method is evaluated against several previously published interpolation methods by using visual examples and root mean square error (RMSE) comparison. We found that the proposed gradient-based interpolation method can achieve better visual results while maintaining a lower RMSE than other interpolation methods under various dynamic ranges of a scene ranging from dim to bright conditions. (C) 2013 Optical Society of America

关键词： Charge coupled devices image processing algorithms Light intensity Polarimetric imaging Underwater imaging Visible light

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Lattice algebra approach to multispectral analysis of ancient documents

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APPLIED OPTICS 2013年第4期52卷 674-682页

作者： Valdiviezo-N, Juan C. Urcid, Gonzalo Univ Politecn Tulancingo Div Ingn Tulancingo 43629 Hidalgo Mexico Inst Nacl Astrofis Opt & Electr Puebla 72000 Mexico

This paper introduces a lattice algebra procedure that can be used for the multispectral analysis of historical documents and artworks. Assuming the presence of linearly mixed spectral pixels captured in a multispectral scene, the proposed method computes the scaled min- and max-lattice associative memories to determine the purest pixels that best represent the spectra of single pigments. The estimation of fractional proportions of pure spectra at each image pixel is used to build pigment abundance maps that can be used for subsequent restoration of damaged parts. Application examples include multispectral images acquired from the Archimedes Palimpsest and a Mexican pre-Hispanic codex. (C) 2013 Optical Society of America

关键词： Digital image processing image processing image processing algorithms Multispectral imaging Reflectance spectroscopy Spectral imaging

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PZT calibration

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OPTIK 2013年第17期124卷 2803-2806页

作者： Ionita, Bogdan Florin Garoi, Florin Logofatu, Petre Catalin Apostol, Dan GSI Darmstadt Helmholtz Ctr Heavy Ion Res D-64220 Darmstadt Germany Natl Inst Laser Plasma & Radiat Phys Lasers Dept Magurele 077125 Romania

One important source of error in phase-shift interferometry consists of a nonuniform application of phase steps, due, for example, to a nonlinear piezoelectric effect in the phase shifter. We developed a method for inline PZT calibration using a video camera for acquiring interferograms and an ATI Radeon X1650 video card for frame processing. The PZT was calibrated over a voltage range of 40 V and a displacement range of 11 mu m. We acquired 801 interferograms in a Twyman-Green interferometer and a 801 x 801 matrix computed from the subtraction of each interferogram from every other interferogram was obtained and used for calibration. The speed and accuracy of frame processing of the video card was compared to the results obtained by an Intel QuadCore processor. In terms of accuracy there are no significant differences, but the processing using the video card was similar to 5 times faster than the processing using the processor. The processing took similar to 5 min and we obtained a dispersion of similar to 10 nm when we fitted the displacement of the PZT to a polynomial of degree 5 in voltage. (C) 2012 Elsevier GmbH. All rights reserved.

关键词： Phase-shift interferometry image processing algorithms

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Demonstration of a multichannel, multiresolution imaging system

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APPLIED OPTICS 2013年第24期52卷 6081-6089页

作者： Belay, Gebirie Y. Ottevaere, Heidi Meuret, Youri Vervaeke, Michael Van Erps, Jurgen Thienpont, Hugo Vrije Univ Brussel Dept Appl Phys & Photon TONA Fac Engn Brussels Photon Team B PHOT B-1050 Brussels Belgium

In conventional multichannel imaging systems, all channels have similar imaging properties [field-of-view (FOV) and angular resolution]. In our approach, channels are designed to have different imaging properties which add multiresolution capability to the system. We have experimentally demonstrated, for the first time to our knowledge, a three-channel imaging system which simultaneously captures multiple images having different magnifications and FOVs on an image sensor. Each channel consists of four aspherical lens surfaces fabricated from four PMMA plates by ultraprecision diamond tooling and of a baffle made from a titanium (Ti) and aluminum (Al) based metal alloy. The integrated imaging system is able to record a FOV of 7.6 degrees with the first channel and 73 degrees with the third channel while having a magnification ratio of about 6 between them. The experimental and simulation results, specifically the FOV and magnification ratios, are comparable, and this paves a way for low-cost, compact imaging systems which can embed smart imaging functionalities. (c) 2013 Optical Society of America

关键词： image processing image processing algorithms image quality Imaging systems Medical imaging Optical design

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Restoring a silhouette of the hand in the problem of recognizing gestures by adaptive morphological filtering of a binary image

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JOURNAL OF OPTICAL TECHNOLOGY 2013年第11期80卷 685-690页

作者： Malashin, R. O. Lutsiv, V. R. OAO SI Vavilov State Opt Inst St Petersburg Russia

algorithms are presented for the adaptive processing of binary images of silhouettes of the human hand obtained by means of color-brightness filters. These algorithms are based on the use of a combination of elementary morphological operations that take into account the direction of the fingers. algorithms are presented for removing noise on binary images that are adapted to the result of the operation of a color filter, and a method is presented for filling internal contours of a silhouette of the hand in order to remove grouped marking errors. The experimental results show that the proposed image-processing method increases the probability of successful detection, tracking of the hand, and recognition of gestures. (C) 2014 Optical Society of America.

关键词： algorithms Color spaces image processing image processing algorithms Imaging noise Metrological instrumentation

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