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。     

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。     

NaCl溶液补偿非平衡热光关联成像系统

热光无透镜鬼成像系统要求物光和参考光两个光路的光程相等,当不满足此条件时,成像质量就会下降。实际应用中热光关联成像系统两臂长度相等的条件极为苛刻,很难满足。笔者设计了一种补偿式热光关联成像系统的实验方案,利用NaCl溶液补偿物光和参考光两个光路的光程差。实验结果表明,将一定浓度的NaCl溶液放在光程较长的光路中,可以有效补偿非平衡系统的光程差,从而获得待测物体清晰的关联像。     

基于数字微镜器件的光子计数对应鬼成像

提出了一种基于数字微镜器件的光子计数对应鬼成像方案。该方案采用数字微镜器件对光源进行调制,通过时间相关单光子计数技术获取光子计数值,并利用对应鬼成像算法计算目标物体的像。结合鬼成像理论和对应鬼成像理论阐明了光子计数对应鬼成像原理,并通过实验对该方案进行了验证。研究结果表明,该方案能够实现弱光成像。利用该方案可以获得与传统鬼成像效果相当的成像质量,但降低了图像重建过程中的计算量和算法复杂度。此外,该方案略去了阵列探测器对光强分布的测量,利用一个不具有空间分辨率的单光子探测器结合对应鬼成像算法,即可得目标物体的像,同时也能获得目标的距离信息。     

强度关联三维衍射层析的实验研究

提出了一种基于强度关联成像的新型三维衍射层析技术.利用强度关联成像技术(鬼成像)可实现无透镜傅里叶变换的特点,并结合衍射层析技术和二步相位恢复算法,使用波长为650 nm的赝热光实现了强度关联三维衍射层析.详细描述了强度关联三维衍射层析的基本原理以及具体实验结果,为在第三代同步辐射光源实现非相干X光衍射成像积累了经验.     

三种不同结构的无透镜鬼成像实验研究(英文)

为实现远距情况下的实际应用,对赝热源鬼成像进行了从透射到反射的实验研究.首先利用CCD的两个独立区域分别探测参考光和信号光,得到双缝的透射型鬼成像,继而利用一个CCD和一个独立的桶探测器分别探测参考臂和物臂的光强信息,通过对没有空间分布的物臂光强和没有经过物体而有空间分布的参考臂光强信号进行关联计算实现透射和反射鬼成像.为设计和研制能进行现场应用的样机系统,以透射结构为例,对成像结果与系统各参数之间的关系进行了详细的对比实验研究,结果表明通过增加采样率、增大光强、适当调节快门时间和光阑大小可以提高成像的分辨率和可见度.     

相位恢复算法在量子关联衍射成像中的应用研究

随着研究工作的逐步深入,目前已经利用经典热光源实现了关联衍射成像,使得该技术有望在X射线以及中子衍射成像等方面得到广泛应用。在实验利用非相干光得到物体无透镜傅里叶变换频谱的基础上,采用误差消除与输入输出恢复算法,并结合过采样理论,实现了实验所用物体透射率函数的恢复。分别得到了纯振幅物体的振幅分布函数与纯相位物体的相位分布函数。此外,还讨论了实验所得傅里叶变换频谱的噪声等因素对图像恢复结果的影响。     

散焦光栅测量光束漂移的光路设计仿真

传统的光束漂移量测量系统利用近、远场测量设备分别测量光束的平漂量和角漂量,结构复杂、实时性低。散焦光栅焦平面处正、负一级衍射斑的位置变化可同时反映光束的平漂量和角漂量,为验证该理论、搭建简化的测量系统需要对光路设计进行仿真。基于散焦光栅的成像机理,利用Matlab软件构建了光束通过散焦光栅的成像模型,仿真结果与理论分析一致;最后对光栅和透镜等不同光路设计参数与最大漂移量测量幅值的关系进行了模拟。结果表明,在成像单元约1 cm2、短焦透镜焦距约12 cm的条件下,为实现漂移量测量精度和可测幅度的最大化,散焦光栅需要离轴15 mm,散焦光栅与短焦透镜的焦距比为6。     

基于迭代重构算法改进晶体衍射分光X射线鬼成像的图像质量研究

X射线鬼成像是一种低剂量、非定域成像方法,对医疗诊断和生物成像具有重要意义.在基于晶体劳厄衍射分光的X射线鬼成像中,晶体振动会造成衍射光路上散斑的模糊,进而导致利用关联方法重构图像衬度和空间分辨的降低.本文系统分析了衍射光路上散斑图像的模糊程度对归一化二阶关联函数g(2)的最大值和半高全。宽的影响.模糊程度的增强会导致g(2)最大值的减小和半高全宽的展宽,在理论上证明了模糊程度会引起重构图像的衬度和分辨能力的降低.为解决上述问题,本文在衍射光路和直通光路的直接关联方法(CLH)的基础上提出C_LHE方法(CLH enhanced method).模拟实验表明C_LHE算法能同时改善图像衬度和提高重构分辨率,并且模糊程度增强时,G_LHE算法重构图像的峰值信噪比与先对直通光路的散斑图像进行高斯滤波处理再进行双光路关联计算方法(GLL)的差距扩大,同时保证其对噪声的鲁棒性.本文为晶体衍射分光的X射线鬼成像的实际应用提供可行的思路.     

基于追踪补偿的运动物体计算关联成像方法

计算关联成像是利用成像物体的反射或透射信号与结构化的参考光进行多次关联成像,具有了灵敏度高、抗干扰能力强等优点。当物体和计算关联成像系统存在相对运动时,在成像过程中物体的反射或透射信号与参考光的光场涨落失去关联性,进而会产生运动模糊。从二阶关联函数的角度推导了运动成像导致模糊的原因以及追踪补偿原理;恢复计算关联成像系统中参考光和桶探测器收集的光强值的关联性,实现了计算关联成像中的追踪补偿策略;计算机仿真解释了计算关联成像光路中对物体平移干扰进行补偿的策略,证实了该追踪补偿方法对运动物体成像的有效性,克服了物体与成像系统之间的相对运动引起的成像质量下降。方法为关联成像对运动物体的识别、跟踪、遥感和实时在线成像提供了技术手段。     

Lensless ghost imaging through the strongly scattering medium

Lensless ghost imaging has attracted much interest in recent years due to its profound physics and potential applications. In this paper we report studies of the robust properties of the lensless ghost imaging system with a pseudo-thermal light source in a strongly scattering medium. The effects of the positions of the strong medium on the ghost imaging are investigated. In the lensless ghost imaging system, a pseudo-thermal light is split into two correlated beams by a beam splitter. One beam goes to a charge-coupled detector camera, labeled as CCD2. The other beam goes to an object and then is collected in another charge-coupled detector camera, labeled as CCD1, which serves as a bucket detector. When the strong medium, a pane of ground glass disk, is placed between the object and CCD1, the bucket detector, the quality of ghost imaging is barely affected and a good image could still be obtained. The quality of the ghost imaging can also be maintained, even when the ground glass is rotating, which is the strongest scattering medium so far. However, when the strongly scattering medium is present in the optical path from the light source to CCD2 or the object, the lensless ghost imaging system hardly retrieves the image of the object. A theoretical analysis in terms of the second-order correlation function is also provided.     

Computational lensless ghost imaging in a slant path non-Kolmogorov turbulent atmosphere

Based on the computational ghost-imaging arrangement with “virtual detector” and the extended Huygens–Fresnel integral, lensless ghost imaging with fully spatially incoherent light radiation through a slant turbulent channel has been studied. The analytical ghost-imaging formulas have been derived. Our formulas shown that the image quality is influenced by the turbulence strength, the propagation distance, the zenith angle of communication channel and the fractal constant of the non-Kolmogorov power spectrum of atmospheric turbulence. In the case of the short-exposure imaging and the bucket detector detection for test field, the influence of the atmospheric turbulence on the quality of the ghost imaging mainly come from the path which is ahead of object.     

Signal-to-noise ratio of lensless ghost interference with thermal incoherent light

Factors influencing the signal-to-noise ratio (SNR) of lensless ghost interference with thermal incoherent light are investigated.Our result shows that the SNR of lensless ghost interference is related to the transverse length of the object,the position of the object in the imaging system and the transverse size of the light source.Furthermore,the effects of these factors on the SNR are discussed in detail by numerical simulations.     

Resolution and visibility of two-color pseudothermal lensless ghost imaging

Two-color (or nondegenerate-wavelength) lensless ghost imaging using pseudothermal light source is investigated theoretically by use of classical optical coherence theory. We find that for two-color pseudothermal lensless ghost imaging the visibility and resolution is determined by (Δ) the product of the wavelength and the corresponding path length rather than the wavelength for each path or the path length. We also confirm our theoretical conclusion by numerical simulations. The result shows we must make a trade-off between resolution and visibility in devise practical experiments, as the resolution of the imaging can be improved by decreasing Δ but with visibility getting poor, and vice versa.     

Ghost telescope and ghost Fourier telescope with thermal light

As important observation tools, telescopes are very useful in remote observations. We report a proof-of-principle experimental demonstration of ghost telescope scheme and show that, by measuring the intensity correlation of two light fields and only changing the position of the detector in the reference path, ghost telescope and ghost Fourier telescope can be obtained even if a single-pixel detector is fixed in Fresnel region of the object. Differences between conventional telescope and ghost telescope are also discussed.     

Lensless diffractive imaging using tabletop coherent high-harmonic soft-X-ray beams

We present the first experimental demonstration of lensless diffractive imaging using coherent soft x rays generated by a tabletop soft-x-ray source. A 29 nm high harmonic beam illuminates an object, and the subsequent diffraction is collected on an x-ray CCD camera. High dynamic range diffraction patterns are obtained by taking multiple exposures while blocking small-angle diffraction using beam blocks of varying size. These patterns reconstruct to images with 214 nm resolution. This work demonstrates a practical tabletop lensless microscope that promises to find applications in materials science, nanoscience, and biology.     

Compressed ghost imaging based on differential speckle patterns

We propose a compressed ghost imaging scheme based on differential speckle patterns,named CGI-DSP.In the scheme,a series of bucket detector signals are acquired when a series of random speckle patterns are employed to illuminate an unknown object.Then the differential speckle patterns(differential bucket detector signals) are obtained by taking the difference between present random speckle patterns(present bucket detector signals) and previous random speckle patterns(previous bucket detector signals).Finally,the image of object can be obtained directly by performing the compressed sensing algorithm on the differential speckle patterns and differential bucket detector signals.The experimental and simulated results reveal that CGI-DSP can improve the imaging quality and reduce the number of measurements comparing with the traditional compressed ghost imaging schemes because our scheme can remove the environmental illuminations efficiently.     

Imaging a periodic moving/state-changed object with Hadamard-based computational ghost imaging

We propose a method for imaging a periodic moving/state-changed object based on computational ghost imaging with Hadamard speckle patterns and a slow bucket detector, named as PO-HCGI. In the scheme, speckle patterns are produced from a part of each row of a Hadamard matrix. Then, in each cycle, multiple speckle patterns are projected onto the periodic moving/state-changed object, and a bucket detector with a slow sampling rate records the total intensities reflected from the object as one measurement. With a series of measurements, the frames of the moving/state-changed object can be obtained directly by the second-order correlation function based on the Hadamard matrix and the corresponding bucket detector measurement results. The experimental and simulation results demonstrate the validity of the PO-HCGI. To the best of our knowledge, PO-HCGI is the first scheme that can image a fast periodic moving/state-changed object by computational ghost imaging with a slow bucket detector.     

Ghost imaging and ghost interference with pseudo-thermal light: Mode-separation by pure software processing

We report on a new experiment in which ghost imaging and ghost interference with quasi-thermal light are simultaneously obtained from the same set of experimental reference patterns. By sliding the mask along the object arm in a continuous way, one can see imaging and diffraction patterns to come to light and fade out in opposite directions.     

Experimental investigation of the quality of lensless super-resolution ghost imaging via sparsity constraints

Ghost imaging via sparsity constraints (GISC) can nonlocally realize super-resolution imaging. Factors influencing the quality of lensless super-resolution GISC are investigated and the experimental results show that, the quality of GISC is enhanced as the object?s sparse ratio in the representation basis or the spatial transverse coherence lengths on the object plane are decreased. The differences between ghost imaging (GI) and GISC are also discussed.