Phase retrieval and coherent diffraction imaging by a linear scanning pinhole sampling array

We propose a new method for phase retrieval and coherent diffraction imaging by a specially designed pinhole sampling array (PSA) based on a liquid crystal spatial light modulation. We demonstrate that the phase and the amplitude of the wave front passing through a pinhole sampling array plate can be directly extracted from the inverse Fourier transform of the far-field diffraction intensity pattern. Scanning the whole surface of the wave front by such a series of the PSA plates, we can assemble the extracted complex amplitude to a two-dimensional discrete distribution of the sampled wave front covering the entire PSA plate plane in the scanning consequence. We called it linear scanning pinhole sampling array (LSPSA). Thus the wave front can be reconstructed which avoids any iterative algorithms. Furthermore, it provides a feasible approach for lensless coherent diffraction imaging in real-time.     

Noniterative phase retrieval from a single diffraction intensity pattern by use of an aperture array

A noniterative method for retrieving the phase of a wave field from a diffraction intensity measurement in a coherent wave field is proposed. In this method, the phase can be calculated from analytic equations based on the properties of entire functions by use of Fourier transforms. This method requires only a single measurement of the intensity of a diffracted wave through an array filter of rectangular apertures and then does not need to use any lens systems and coherent reference waves. Therefore, it provides a potentially useful means for coherent imaging in a wide class of wave fields such as optical, x ray, electron, and atomic waves.     

Phase retrieval using an aperture-array filter under partially coherent illumination

Recently we have proposed a deterministic phase retrieval method using an aperture-array filter to reconstruct a complex-valued object from a single diffraction intensity pattern. We describe here the effect of quasi-monochromatic partially coherent illumination on the object reconstruction by the phase retrieval method, and then present the method of eliminating the effect of the partially coherent illumination from the diffraction intensity pattern via a simple Fourier deconvolution operation provided that the complex degree of spatial coherence of the illuminating beam is known. The usefulness of this method is shown in computer-simulated examples of the object reconstructions under Gaussian Schell-model partially coherent illumination.     

基于光栅分光法的相干衍射成像

提出一种可以通过单次曝光实现 PIE(ptychographic imaging engine)成像的方法, 该方法用正交光栅将入射细光束衍射为传播方向不同的子光束簇以对样品进行照明, 并用CCD同时记录各个子光束所形成的衍射光斑阵列. 该方法很好地克服了现有PIE方法的成像质量易受机械扫描误差影响和数据采集时间过长两个缺点, 具有很好的实用价值. 关键词： 相干衍射成像 相位恢复 显微成像 迭代算法     

Optical image encryption based on coherent diffractive imaging using multiple wavelengths

Coherent diffractive imaging is an optical technique in which the information of an object is encoded in the diffraction intensity using a single-path wave propagation strategy. In recent years, coherent diffractive imaging has attracted much attention in many fields due to its marked advantages, such as robustness to vibration and the suitability for various wavelengths. In this paper, we propose to apply coherent diffractive imaging using multiple wavelengths for optical image encryption. A light wavelength is tuned during the encryption, and a series of diffraction intensity maps (i.e., ciphertexts) is sequentially recorded in the Fresnel domain. During image decryption, an iterative retrieval algorithm is further developed, and cryptosystem security and robustness of the proposed method are also analyzed. Numerical simulation results are presented to demonstrate feasibility and effectiveness of the proposed method.     

Phase-coded aperture for optical imaging

For the optical spectrum region, we describe a novel phase-coded aperture imaging system that can be used in a computational imaging camera. The optical design includes a phase-only screen followed by a detector array. A specific diffraction pattern forms at the detector array when the wavefront from a point source object passes through the phase screen. Since diffraction effects cannot be ignored in the optical regime, an iterative phase retrieval method is used to calculate the phase coded screen. Correlation type processing can be applied for the image recovery. Computer simulation results are presented to illustrate the excellent imaging performance of this camera.     

Generation of optical vortices with arbitrary shape and array via helical phase spatial filtering

We report a method for generation of arbitrary shape and array of optical vortices by use of a superposition of coherent elementary vortices based on helical phase spatial filtering in spatial frequency domain. In this method, a helical phase spatial filter (HPSF) is placed in the spatial frequency plane of a 4-f imaging processing system. We demonstrated that the output field distribution represents the convolution between the input field and an elementary vortex field introduced by the HPSF, which results in a special shape or array of optical vortices determined by the “degenerate” properties of coherent elementary vortices and the distribution formats of the input field.     

Generalized eikonal of partially coherent beams and its use in quantitative imaging

The generalized eikonal of a partially coherent paraxial wave is introduced via a differential equation describing the evolution of the time-averaged intensity. The theoretical formalism provides an analytical tool for the study of partially coherent imaging systems. It also makes possible quantitative phase retrieval and compositional mapping of weakly absorbing samples using phase-contrast imaging with broadband polychromatic radiation of known spectral distribution. An experimental demonstration is presented of the quantitative reconstruction of the projected thickness of a sample, given a phase-contrast image obtained using a polychromatic microfocus x-ray source.     

Linear algorithms for phase retrieval in the Fresnel region. 2. Partially coherent illumination

Analytical expressions for the spatial distribution of the spectral density and intensity of projection images are derived for a broad class of object transmission functions in the case of partially coherent Schell-model-type incident illumination. The expressions are linear with respect to the phase distribution in the transmitted wave. Associated methods for phase retrieval are discussed with the emphasis on a technique that allows simultaneous “automatic” phase retrieval and deconvolution of projection images of homogeneous objects by means of mutual cancellation at a specified defocus distance of the Fresnel diffraction effects and the image blurring due to the point-spread function of the imaging system.     

Instability of Solution of Phase Retrieval in Direct Diffraction Phase-Contrast Imaging with Partially Coherent X-Ray Source

The theoretical model of direct diffraction phase-contrast imaging with partially coherent x-ray source is expressed by an operator of multiple integral. It is presented that the integral operator is linear. The problem of its phase retrieval is described by solving an operator equation of multiple integral. It is demonstrated that the solution of the phase retrieval is unstable. The numerical simulation is performed and the result validates that the solution of the phase retrieval is unstable.     

134-W phase locking of two-dimensional four-fiber lasers with improved self-imaging resonator

We experimentally demonstrate the phase locking of a two-dimensional （2D） array of four fiber lasers using an improved self-imaging resonator with a spatial filter. The high visibility interference round stripes of the coherent beam profile are observed. The coherent output power of the fiber array exceeds 134 W. Tile entire system operates quite stably, and no thermal effects observe in the spatial filter, indicating that the coherent output power can be increased using this method.     

相位恢复测量长焦距镜面

针对长焦距光学镜面检测中测量光路长,振动干扰较大,不容易用干涉仪进行面形检测的难题,提出了一种基于相位恢复技术的测量方法.该方法用相干点光源照射被测镜,采集一系列焦点附近的衍射光强图像,然后运用相位恢复算法得到镜面面形误差分布.利用衍射光学理论建立了测量模型,并用基于Gerchberg-Saxton算法的迭代算法求解模型.然后仿真验证了光场传播模型的可靠性和测量算法的有效性,并用该方法测量了一块曲率半径8 700 mm,口径145 mm的球面镜.通过对光强图像位置进行优化,并选择适当离焦位置的图像,最终恢复出了镜面面形.相位恢复测量的结果与动态干涉仪测量结果基本一致,并且测量装置简单,对环境要求低.     

相位恢复测量长焦距镜面(英文)

针对长焦距光学镜面检测中测量光路长,振动干扰较大,不容易用干涉仪进行面形检测的难题,提出了一种基于相位恢复技术的测量方法.该方法用相干点光源照射被测镜,采集一系列焦点附近的衍射光强图像,然后运用相位恢复算法得到镜面面形误差分布.利用衍射光学理论建立了测量模型,并用基于Gerchberg-Saxton算法的迭代算法求解模型.然后仿真验证了光场传播模型的可靠性和测量算法的有效性,并用该方法测量了一块曲率半径8700mm,口径145mm的球面镜.通过对光强图像位置进行优化,并选择适当离焦位置的图像,最终恢复出了镜面面形.相位恢复测量的结果与动态干涉仪测量结果基本一致,并且测量装置简单,对环境要求低.     

Phase imaging from a diffraction pattern in the presence of vortices

We investigate phase imaging from a diffraction pattern in the presence of vortices. In particular we demonstrate that a difference map method for phase retrieval which contains a support constraint does not necessarily conserve the net topological charge of the trial wave field. Hence, no a priori information regarding the charges of the vortices is required for a successful phase retrieval.     

相干X射线衍射成像三维重建的数字模拟研究

利用相干X射线衍射成像“过采样”采集样品的远场相干衍射图样, 结合相位重建迭代算法重建物空间样品信息. 三维重建过程中, 边界约束条件是相位重建算法中最为关键的部分. 本文采用数字模拟的方法, 利用灰度值图像作为物空间的样品, 研究并实现了边界条件的自动寻找, 重建结果显示比以往采用较“松”的边界约束更为精确. 利用噪声模拟方法, 研究了衍射图样中不同噪声类型的滤除对重建结果的影响. 研究发现传统的去噪方法在高噪声情况下不能直接应用于相干X射线衍射成像, 并找到了适用于相干X射线衍射成像噪声滤除的有效方法. 研究表明, 此方法能非常有效地降低噪声对重建结果的影响. 利用模拟三维纳米金颗粒作为样品, 完成了对纳米金颗粒中电子密度分布的三维重建, 在有随机噪声的影响下, 也得到了很好的重建结果, 并找到了成功实现三维重建的噪声限为信噪比不低于27. 关键词： X射线相干衍射成像 过采样 三维相位重建 显微成像     

菲涅耳数字全息成像系统的脉冲响应分析

数字全息成像由CCD记录数字全息图后经过计算机数值重建物光波场,这个过程从傅里叶变换角度看等同于数字全息图的频谱分析。讨论了数字成像系统的脉冲响应函数,并分别推导了其实像、虚像、零级像在平面波和球面波照射下的波前复振幅分布。结果表明,实像和虚像是移位的夫琅和费衍射分布,而零级像是CCD光瞳的菲涅耳衍射分布,且与参考光波前分布无关。     

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.     

Retrieval of the atomic displacements in the crystal from the coherent X‐ray diffraction pattern

The retrieval of spatially resolved atomic displacements is investigated via the phases of the direct(real)‐space image reconstructed from the strained crystal's coherent X‐ray diffraction pattern. It is demonstrated that limiting the spatial variation of the first‐ and second‐order spatial displacement derivatives improves convergence of the iterative phase‐retrieval algorithm for displacements reconstructions to the true solution. This approach is exploited to retrieve the displacement in a periodic array of silicon lines isolated by silicon dioxide filled trenches.     

利用扩散场信息的超声兰姆波全聚焦成像

利用兰姆波的扩散场信号,实现了距离传感器较近缺陷的全聚焦成像.通过两传感器接收的扩散场全矩阵信号进行互相关,恢复出两传感器之间的格林函数响应,重建新的全矩阵.该重建全矩阵削弱了直接耦合采集响应信号中存在的早期饱和非线性效应信号,恢复了被遮盖的近距离缺陷散射信号.在含缺陷的各向同性铝板中激发兰姆波,重建信号的早期信息与直接俘获信号的后期信息相结合形成混合全矩阵,结合全聚焦成像,优化成像效果.所提方法为薄板类结构中距离传感器较近缺陷的兰姆波无损检测提供了理论指导.     

Nanoscale imaging with resonant coherent X rays: extension of multiple-wavelength anomalous diffraction to nonperiodic structures

The methodology of multiple-wavelength anomalous diffraction, widely used for macromolecular structure determination, is extended to the imaging of nonperiodic nanostructures. We demonstrate the solution of the phase problem by a combination of two resonantly recorded coherent scattering patterns at the carbon K edge (285 eV). Our approach merges iterative phase retrieval and x-ray holography approaches, yielding unique and rapid reconstructions. The element, chemical, and magnetic state specificity of our method further renders it widely applicable to a broad range of nanostructures, providing a spatial resolution that is limited, in principle, by wavelength only.