基于压缩感知超分辨鬼成像

分辨率是成像系统的一个重要参数, 获得高分辨率图像一直是鬼成像系统的一个目标. 本文提出了以成像系统点扩散函数作为先验知识, 基于稀疏测量的超分辨压缩感知鬼成像重建模型. 搭建了一套计算鬼成像实验装置, 用于验证该模型对于提高鬼成像系统分辨率的有效性, 并与传统的鬼成像计算模型进行了对比. 实验表明, 利用该模型可突破成像系统衍射极限分辨率的限制, 得到超分辨鬼成像. 关键词： 鬼成像 压缩感知 超分辨 稀疏测量     

散焦对无透镜鬼衍射和传统成像的影响

散焦一直是影响成像系统成像质量的主要问题之一。分析了不同光路上存在散焦对无透镜鬼衍射成像的影响,比较了散焦对无透镜鬼衍射成像和传统成像两者之间的差异。在前期理论研究基础上,对无透镜鬼衍射和传统成像的强度函数做了进一步分析,结果表明散焦的效果相当于物体的透射函数在相位上增加一个啁啾调制,使得两种成像系统在一定程度上是等价的。     

探测器大小与散焦对无透镜鬼衍射的影响

近年来,基于热光场的鬼成像在理论和实验上得到了广泛的关注。研究了探测器尺寸大小以及探测光路距离不相等(即散焦)对无透镜鬼衍射成像的影响。在以前的理论工作基础上,对无透镜鬼衍射成像的强度关联函数做了进一步的分析,发现散焦的效果相当于使物体的透射函数在相位上有一个啁啾调制,而有限大小的探测器则使得无透镜鬼衍射系统等价于一个部分相干成像系统,两者都会引起成像质量的降低。通过计算不同条件下的成像相关度,定量分析了不同参数下的无透镜鬼衍射的成像质量,为具体的实验设计提供定量的帮助。     

大望远镜系统衍射极限倍数的确定

利用大气湍流的光学相关函数确定湍流光学相关时间，并在此时间内通过成像系统的光学传递函数修正大气湍流效应后定标大望远镜(500mm口径，500m焦距)系统衍射极限倍数。     

湍流大气成像系统分辨率的研究

采用基于Kolmogorov 1941串级湍流模型建立的调制湍流折射率谱模型、简单透镜成像系统传递函数的高斯函数近似和平方近似,从理论上分析了大气成像系统的光学传递函数,研究了有限湍流尺度(湍流内、外尺度)对湍流大气中成像系统光学分辨率的影响。给出了成像系统长曝光光学传递函数和积分分辨率的近似解析关系。结果表明在采用大孔径成像系统成像时,应该考虑湍流尺度对大气系统成像的作用。     

无衍射光束提高成像系统分辨率

设计了一种在非相干光源下利用轴棱锥产生的无衍射光束成像系统.基于衍射积分理论与点扩散函数推导出成像系统分辨率的表达式,利用光学软件对无衍射光束成像系统的初始结构模型进行仿真,并以蓝光LED作为光源,将条纹状物体、透镜组以及轴棱锥等光学元件组合为成像系统进行实验.结果表明:实验结果与理论分析相符,即非相干光源无衍射Bessel光束成像系统利用无衍射光束的特性能够提高成像分辨率.     

实验研究探测器大小与散焦长度对无透镜鬼衍射的影响

无透镜鬼衍射是一种特殊的非局域关联成像技术,通过对包含物体信息的测试光路和不含物体信息的参考光路的光场强度涨落关联进行测量,在参考光路上可得到物体的衍射图样。利用赝热光源实验研究了探测器尺寸大小和光路散焦长度对无透镜鬼衍射质量的影响。实验以四缝物体为例,定量研究了探测器大小和散焦是如何改变无透镜鬼衍射的成像结果,并和理论模拟进行了比较,获得了比较一致的结果。利用图像相关度定量分析了实验结果与理想无透镜鬼衍射图像的差别,发现这两者都会使无透镜鬼衍射的质量变差。     

非制冷长波红外热像仪折衍混合双视场光学系统设计

根据衍射光学元件具有大的负向色散特性,将衍射光学元件应用于红外双视场光学系统中,根据傅里叶光学分析衍射光学元件(DOE)的消色差,列表对比折射透镜与衍射光学透镜的特性,并给出变倍比为4∶1可用作非制冷红外热像仪的光学系统的具体设计实例.系统采用切入式变焦方式,在短焦时切入2片透镜实现宽视场,通过引入二元面和非球面提高了成像质量.设计结果表明:在空间频率11 lp/mm处,短焦距40 mm时,各个视场的MTF值均大于0.6;长焦距160 mm时,各个视场的MTF值均大于0.7,宽视场和窄视场都具有较好的成像质量.     

利用CCD准确测量激光远场发散角

 利用CCD面阵接收器,通过标定的方法,将其准确安置在长焦距透镜后焦面上,并找出CCD 象元数与原场发散角的对应关系,从而迅速确定远场发散角。同时用短焦距透镜对 光束限制光阑成像,测得近场光斑光强分布。以激光束振幅函数的傅里叶变换作为理想衍射 极限,将远场发散角与之比较,可以得到用几倍衍射极限的方法表示的实际光束质量。     

新型衍射光学成像光谱仪的设计和分析

为了克服在传统衍射光学成像光谱仪中,衍射透镜的焦距随波长变化引起系统放大率随波长变化,从而导致光谱图像的像元配准误差,得到并不精确的相对光谱信号强度,提出了将衍射透镜与消色差透镜系统相结合的新型折/衍混合、二组元复合远心成像光学系统的技术方案,具体分析推导了该系统的成像理论.在此理论指导下,利用光学设计软件Zemax设计了一套可见近红外成像光谱仪光学系统.结果表明,不但系统的放大率不随波长变化,而且进一步降低了衍射透镜的加工难度,改进了衍射光学成像光谱仪的光学性能,为新型衍射光学成像光谱仪的研制提供了重要的理论依据和设计指导.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.     

Fiber Modal Index Measurements Based on Fiber Gratings

A novel method based on fiber gratings for measuring the effective indices of fiber modes is proposed. The effective index difference between the core mode and a cladding mode was obtained by analyzing the interference fringe of a pair of cascaded long-period fiber gratings. In order to extract the core mode index from the measured index difference, an index matching oil immersion method is proposed. By analyzing the interaction between the cladding mode and the oil applied on the cladding surface, the mode order and the effective index of the involved cladding mode might be calculated. Experimental results about the interference fringe shifts induced by the oil index and the oil-applied length are also presented.     

Optical Pulse Compression Schemes That Use Nonlinear Bragg Gratings

Nonlinear optical pulse compression of picosecond pulses typically requires long lengths of optical fiber and multiple components. Periodic structures, such as fiber Bragg gratings, are highly dispersive at wavelengths outside of the photonic bandgap. This implies that such gratings can be used as very short all-fiber compressors. In this paper a number of such compression schemes are reviewed involving uniform and nonuniform fiber Bragg gratings, relying on both soliton and nonsoliton compression principles. Experimental results supporting the corresponding underlying theory are also presented. Finally, an extension of one of the compression schemes is shown, which allows the generation of adjustable high-repetition rate soliton trains.