Ghost imaging with broad distance

We present a scheme that is able to achieve the ghost imaging with broad distance. The physical nature of our scheme is that the different wavelength beams are separated in free space by an optical media according to the slow light or dispersion principle. Meanwhile, the equality of the optical distance of the two light arms is not violated. The photon correlation is achieved by the rotating ground glass plate(RGGP) and spatial light modulator(SLM), respectively. Our work shows that a monochromic ghost image can be obtained in the case of RGGP. More importantly, the position(or distance) of the object can be ascertained by the color of the image. Thus, the imaging and ranging processes are combined as one process for the first time to the best of our knowledge. In the case of SLM, we can obtain a colored image regardless of where the object is.     

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.     

Lensless two-color ghost imaging from the perspective of coherent-mode representation

The coherent-mode representation theory is firstly used to analyze lensless two-color ghost imaging. A quite complicated expression about the point-spread function(PSF) needs to be given to analyze which wavelength has a stronger affect on imaging quality when the usual integral representation theory is used to ghost imaging. Unlike this theory, the coherent-mode representation theory shows that imaging quality depends crucially on the distribution of the decomposition coefficients of the object imaged in a two-color ghost imaging. The analytical expression of the decomposition coefficients of the object is unconcerned with the wavelength of the light used in the reference arm, but has relevance with the wavelength in the object arm. In other words, imaging quality of two-color ghost imaging depends primarily on the wavelength of the light illuminating the object. Our simulation results also demonstrate this conclusion.     

基于反射型物体的高阶非相干热光源关联成像性能研究

现有基于热光源的关联成像主要是针对透射型物体,这样可简化关联成像分析过程。然而对于成像的实际应用,比如遥感技术,反射型物体将具有更大的实用价值。基于非相干均亮的热光源,对反射型物体的高阶关联成像进行了研究,推导出其高阶反射关联成像的关联函数、可见度及信噪比的解析式;对比二阶反射关联成像,讨论阶数对关联成像性能的影响。研究结果表明,对于反射型物体的关联成像,随着阶数的增加,成像的可见度得到提高,但信噪比下降,同时能够通过增加测量次数增加成像的信噪比。     

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.     

Three-dimensional ghost imaging based on periodic diffraction correlation imaging

We experimentally demonstrate a three-dimensional （3D） ghost imaging method based on period diffraction correlation imaging. Compared with conventional ghost imaging, our method can easily retrieve the images of different focal planes. Due to the correlation between the disturbed object beam and the reference beams which do not pass through any scattering, the clear images can be periodically obtained in the uncovered zones even through a scattering medium. The analysis of the 3D imaging resolution reveals that the proper resolution for actual demand can be achieved by designing our devices. The implementation of this experiment is quite simple and low-cost. It facilitates the practical applications of ghost imaging.     

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.     

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。     

Robust Ghost Imaging Based on Degenerate Spontaneous Parametric Down-Conversion

In traditional ghost imaging, the entangled photon pairs produced from the spontaneous parametric down conversion(SPDC) process are used. There is an intrinsic disadvantage that the utilization efficiency of the photon pairs is very low. Inasmuch as all the correlated photon pairs produced by the degenerate SPDC process can be used to record the image of an object, the ghost imaging scheme we present here has a higher utilization efficiency of the photon pairs. We also investigate the robustness of our experimental scheme. The experimental results show that, no matter whether the photon-pair source is two light cones or two beam-like spots, the clear image of the object can be obtained. The slight rotation of the nonlinear crystal has no influence on the imaging quality.Our experimental results also demonstrate that when the part of the photon-pair source in the signal path or the idler path is blocked by unwanted things, the clear ghost image of the object can still be recorded.     

Effects of light intensity on reflective ghost imaging

In this letter, we analyze the effects of light intensity find that the brightness of reflective ghost image can on reflective ghost imaging with thermal source. We be changed by modulating the light intensity of the source and the splitting ratio of the beam splitter. The signal-to-noise ratio will be improved by increa.sing the light intensity of the source. More important, we can obtain the reflective ghost image with high image quality by adopting a low light intensity signal beam and a high light intensity reference beam, which is better than the classical optical imaging, because it can reduce the effects of light on the object.     

Compressed ghost edge imaging

In this Letter, we propose an advanced framework of ghost edge imaging, named compressed ghost edge imaging(CGEI). In the scheme, a set of structured speckle patterns with pixel shifting illuminate on an unknown object.The output is collected by a bucket detector without any spatial resolution. By using a compressed sensing algorithm, we obtain horizontal and vertical edge information of the unknown object with the bucket detector detection results and the known structured speckle patterns. The edge is finally constructed via twodimensional edge information. The experimental and numerical simulations results show that the proposed scheme has a higher quality and reduces the number of measurements, in comparison with the existing edge detection schemes based on ghost imaging.     

Color ghost imaging via sparsity constraint and non-local self-similarity

We propose a color ghost imaging approach where the object is illuminated by three-color non-orthogonal random patterns. The object’s reflection/transmission information is received by only one single-pixel detector, and both the sparsity constraint and non-local self-similarity of the object are utilized in the image reconstruction process. Numerical simulation results demonstrate that the imaging quality can be obviously enhanced by ghost imaging via sparsity constraint and nonlocal self-similarity(GISCNL), compared with the reconstruction methods where only the object’s sparsity is used. Factors affecting the quality of GISCNL, such as the measurement number and the detection signal-to-noise ratio, are also studied.     

Simple time-domain optical method for estimating the depth and concentration of a fluorescent inclusion in a turbid medium

A simple time-domain optical method for estimating the depth and concentration of fluorescent inclusions in turbid media is described. We demonstrate direct depth estimation of a localized fluorescent object from the temporal position of the temporal point-spread function maximum. The depth estimation permits recovery of the fluorophore concentration, both of which are essential quantities for optical molecular imaging studies. Since the maximum is independent of the fluorophore concentration, excitation laser power, detector gain, and other system-dependent factors, this method ensures a robust and efficient approach.     

Laser trapping of small colloidal particles in a nematic liquid crystal: clouds and ghosts

We show that, contrary to intuition, small (< or =1 microm) transparent particles can be trapped and manipulated in a nematic liquid crystal using an intense laser beam, although their index of refraction is lower than both refractive indices of the surrounding birefringent fluid. Two mechanisms are identified that are responsible for this anomalous trapping: (i) surface-induced distortion of the birefringent media around the particle, creating a high-index "cloud" around the colloid, and (ii) laser-induced distortion or (partial) melting of a nematic, creating a ghost colloid.     

Multi-Path Ghost Imaging by Means of an Additional Time Correlation

Ghost imaging functions achieved by means of the spatial correlations between two photons is a new modality in imaging systems. With a small number of photons, ghost imaging is usually realized based on the position correlation of photon pairs produced from the spontaneous parametric down-conversion process. Here we demonstrate a way to realize multi-path ghost imaging by introducing an additional time correlation. Different delays of paths will induce the shift of the coincidence peak, which carries the information about objects. By choosing the suitable coincidence window, we obtain images of three objects simultaneously, with a visibility of 87.2%.This method provides insights and techniques into multi-parameter ghost imaging. It can be applied to other correlated imaging systems, for example, quantum spiral imaging.     

Quantum crossing symmetry as heart of ghost imaging

In this paper it is proved that the keys to understanding the ghost imaging are the crossing symmetric (CS) photon reactions in the nonlinear media. So CS introduced a real optical path between the object and his “ghost” image, making possible to apply the geometric optics for a rigorous proof of the essential laws of the “ghost” imaging phenomena. Hence, the laws of the plane quantum mirror (QM) and that of spherical quantum mirror, observed in the ghost-imaging experiments, are shown that can be obtained as natural consequences of the energy-momentum conservation laws. So, it is proved that the ghost imaging laws depend only on the energy-momentum conservation and not on the photons entanglement. Using DFG-typical features we obtained explicit predictions of the intensities of the idler photons in terms of the intensities of the interacting photon-(p and s)-beams in the nonlinear crystal. Two fundamental experiments for a decisive test of the [SPDC-DFG]-quantum mirrors are suggested.     

菲涅耳波带板无运动卷积全息术

提出了菲涅耳波带板(FZP)无运动卷积全息术.该技术使用均匀扩展光源,使得从光源不同位置发出的光在经过FZP编码孔径之后,在物体上形成多个菲涅耳波带板投影叠加.物体的全息图是FZP投影光强分布函数与物体的光强分布函数的卷积,无需机械运动便得到物体的扫描全息图.采用数字相关解码方法实现全息图的再现.用蒙特卡罗方法模拟了菲涅耳波带板入射光束在经过散射介质以后,其出射光强分布随散射介质厚度的变化规律.结果表明:当散射介质厚度为5 cm时,出射光束依然基本保持菲涅耳波带板形式的光强分布.对嵌埋在浓度为1%的Intralipid散射溶液中直径为0.4mm的金属丝进行成像实验,分别得到当散射介质厚度为1cm、3cm和5cm时的再现像,实验验证了菲涅耳波带板无运动卷积全息术用于高散射介质中物体成像的可行性.     

基于统计光学的无透镜鬼成像数值模拟与实验验证

作为量子信息领域分支的鬼成像,由于物体的像将出现在不包含物体的光路上的特点,使得这一领域的研究引人入胜。一度认为,只有基于纠缠态双光子的纠缠光源,才能实现鬼成像;但近年来的研究表明,经典热光场也能实现这一过程。从经典统计光学入手,建立了热光场的数值模型,模拟符合热光特性的光场变化、光场传播、以及物体透射函数对热光场的调制,进而从光强度起伏的关联函数中,分别重现振幅型物体和纯相位型物体的傅里叶变换图像;通过与真实实验结果的对比,表明基于统计光学原理的该数值模型所预测的实验结果,与真实的实验结果完全一致。     

Imaging Transparent Objects in a Turbid Medium Using a Femtosecond Optical Kerr Gate

A femtosecond optical Kerr gate time-gated ballistic imaging method is demonstrated to image a transparent object in a turbid medium. The shape features of the object are obtained by time-resolved selection of the ballistic photons with different optical path lengths, the thickness distribution of the object is mapped, and the maximum is less than 3.6%. This time-resolved ballistic imaging has potential applications in studying properties of the liquid core in the near field of the fuel spray.     

Temporal ghost imaging of a time object,dispersion cancelation,and nonlocal time lens with bi-photon state

We present a theory of temporal diffraction, temporal imaging of a bi-photon state, and temporal ghost imaging of a time object. By applying factional Fourier transform to the bi-photon wave packet propagating in space, we could obtain a theory that shows the physical origin of dispersion cancelation, temporal imaging, nonlocal effects of time lenses, and temporal ghost imaging. We introduce the temporal diffraction distance for bi-photon wave packet and show that the bi-photon wave packet behaves like a single wave packet whose temporal diffraction distance is determined by the coherent sum of the temporal diffraction distances for the signal and the idler beams. This property yields the well known dispersion cancelation, the recovery of original bi-photon wave packet in temporal imaging, and the nonlocal combination of two time lenses placed in different arms. We also propose a method for ghost imaging of an arbitrary time object.