X射线菲涅耳波带板成像和投影式相衬成像的数值模拟比较

通过解析分析和数值模拟,比较了钛K线（4.5 keV）与铜K线（8.0 keV）等X射线源背光透视物体情况下,菲涅耳波带板直接成像与投影式相衬成像对被透视物体的空间分辨能力。结果表明,波带板成像可实现优于1 m的高空间分辨能力,而且使用较大尺度背光源更有利于成像。对于高透射或弱吸收的透视物体,波带板难以成像,可采用投影式相衬成像实现m级空间分辨。计入了以前文献没有考虑到的更高阶影响后,解析给出了点光源照射下相衬像的强度分布与对比度。模拟了微焦点X射线源照射存在厚度起伏的薄膜靶以及密度空间调制靶的相衬成像,点光源情况下模拟结果和解析结果相符。讨论了光源大小、成像距离等参数对相衬成像对比度和空间分辨能力的影响,结果表明,通过减小光源尺度和调节物体到探测面的距离,空间分辨能力可优化到1～4 m。     

菲涅耳非相干数字全息大视场研究

菲涅尔非相干相关全息术(Fresnel incoherent correlation holography, FINCH)通过空间光调制器(spatial light modulator, SLM)将来自物点的光波分解为曲率半径不同的两束自相干光,干涉条纹由CCD记录.由于受限于SLM与CCD的像素数目及像素尺寸, FINCH技术与光学全息术相比记录视场要小得多.本文通过对FINCH系统的记录过程进行理论分析,给出了SLM所能记录的视场角,说明通过调控加载在SLM上的双透镜光轴中心,能够扩大SLM的有效直径从而将SLM的有效记录范围增大2.77倍,有效扩大了系统的记录视场.搭建了非相干光反射式数字全息记录系统并对理论分析进行了实验验证,结果表明:在SLM上依次加载不同光轴中心位置的双透镜掩模进行FINCH记录及再现,将得到的各子图像拼接融合可以得到高分辨率大视场图像,为菲涅尔非相干全息术在高分辨大视场显微成像的进一步应用提供了有力支撑.     

菲涅耳波带板应用于聚变靶的高分辨X射线成像分析

在惯性约束核聚变研究中,为了实现1μm高空间分辨keV-X射线成像,文中发展了菲涅耳波带板(FZP)直接成像的分析方法,并通过数值计算研究了FZP的成像特性.针对钛K_α线(光子能量4.51 keV,波长0.275 nm),提出了FZP参数,对制作技术的要求较低.研究了靶尺度的影响.FZP的有效视场使它能够对数毫米大尺度靶实现高分辨成像.还研究了入射光的光谱带宽对成像的影响.FZP的色差有助于单色成像,但是带宽超过限度会导致像的反衬度降低.这些结果表明FZP应用于聚变点火靶的高空间分辨X射线成像的能力,也为应用提出了要求. 关键词： X射线成像 惯性约束核聚变 菲涅耳波带板     

Fresnel波带板编码成像技术

 介绍了Fresnel波带板编码成像原理,并设计出高空间分辨率的Fresnel波带板编码相机,用双孔可见光源对编码相机的成像进行了实验研究,表明该编码相机可以真实地还原源区的空间大小和形状。     

相位型波带板应用于大尺度X射线源成像的分析与模拟

针对大尺度物体的keV-X射线高分辨成像,分析了相位型菲涅耳波带板(FPZP)对物平面1mm区域内点源的成像,确定像的空间分布具有不变性,提出了一种FPZP对扩展光源成像的计算方法.使用这一方法,模拟了放大倍数为10的典型实验条件下最外环宽0.35 μm的FPZ对扩展单色光源的成像.结果表明,随着扩展光源尺度的增加,像的对比度降低.FPZP的负1级和0级衍射是导致像的背景增强和对比度降低的主要因素,并相应导致成像对物方的空间分辨能力下降.对于强度空间分布为正弦调制、对比度为1的1mm尺度方形光源,像的对比度低于0.4,物方分辨能力为0.75 μm.     

Compressive optical image watermarking using joint Fresnel transform correlator architecture

A new optical image watermarking technique based on compressive sensing using joint Fresnel transform correlator architecture has been presented. A secret scene or image is first embedded into a host image to perform optical image watermarking by use of joint Fresnel transform correlator architecture. Then, the watermarked image is compressed to much smaller signal data using single-pixel compressive holographic imaging in optical domain. At the received terminal, the watermarked image is reconstructed well via compressive sensing theory and a specified holographic reconstruction algorithm. The preliminary numerical simulations show that it is effective and suitable for optical image security transmission in the coming absolutely optical network for the reason of the completely optical implementation and largely decreased holograms data volume.     

菲涅耳波带板X射线成像的快速计算方法

菲涅耳波带板直接成像,应用到激光等离子体或惯性约束聚变靶的X射线成像诊断,可实现m甚至亚m的空间分辨能力。在对成像进行数值模拟时,考虑到光源的光谱带宽和几何尺度对成像的影响,要进行菲涅耳-基尔霍夫衍射积分与卷积等数值计算,需占用大量计算机内存并且耗费运行机时。改进了数值计算方法,采用了蒙特卡罗积分法和新的卷积算法。模拟了菲涅耳波带板对大尺度多色X射线源的二维成像,新算法与以往算法相比,可显著减少运算机时,在台式机上实现模拟成像的快速计算。结果表明随着光源尺度增大、光谱带宽增加,像的背景增强,导致反衬度与成像质量下降。     

基于菲涅耳衍射的无透镜相干衍射成像

相干衍射成像是一种新型的无透镜成像技术,在光学测量、显微成像和自适应光学等领域有重要应用．本文提出一种基于单幅菲涅耳衍射强度图样的无透镜相干衍射成像方法;该方法采用特殊设计的卷积可解阵列抽样屏,通过对抽样物波的菲涅耳衍射强度图样进行非迭代的逆菲涅耳变换和滤波等数字处理实现被测物波复振幅信息的恢复,最后通过数字衍射得到物体的数字再现像．文中对抽样孔径、衍射距离、图像传感器尺寸等参数对再现像的影响进行了理论分析和模拟实验研究．发现在针孔大小和记录孔径大小一定的条件下,存在一个最佳的衍射距离;衍射距离过大会给重建图样带来噪声,衍射距离过小则会使再现象的分辨率降低．文中还对抽样针孔大小对系统成像分辨率的影响进行了分析,为进一步开展相关实验研究和应用提供了理论依据．     

A method of hard X‐ray phase‐shifting digital holography

A new method of phase‐shifting digital holography is demonstrated in the hard X‐ray region. An in‐line‐type phase‐shifting holography setup was installed in a 6.80 keV hard X‐ray synchrotron beamline. By placing a phase plate consisting of a hole and a band at the focusing point of a Fresnel lens, the relative phase of the reference and objective beams could be successfully shifted for use with a three‐step phase‐shift algorithm. The system was verified by measuring the shape of a gold test pattern and a silica sphere.     

Fresnel zone plate with apodized aperture for hard X‐ray Gaussian beam optics

Fresnel zone plates with apodized apertures [apodization FZPs (A‐FZPs)] have been developed to realise Gaussian beam optics in the hard X‐ray region. The designed zone depth of A‐FZPs gradually decreases from the center to peripheral regions. Such a zone structure forms a Gaussian‐like smooth‐shouldered aperture function which optically behaves as an apodization filter and produces a Gaussian‐like focusing spot profile. Optical properties of two types of A‐FZP, i.e. a circular type and a one‐dimensional type, have been evaluated by using a microbeam knife‐edge scan test, and have been carefully compared with those of normal FZP optics. Advantages of using A‐FZPs are introduced.     

X射线荧光全息术中消除光源偏振效应和孪生像的重构新算法

以27个铁原子成立方排列的晶体结构为模型,通过数值模拟和重构,讨论了入射光源的偏振性对原子像的影响.结果表明,入射光源的偏振性对原子像的可观测性有非常重要的影响.为此,提出了一种能同时消除光源偏振性影响和全息成像所固有的孪生像的数字重构新算法,并通过数字模拟及重构,结果证明了这是一种有效的数字重构算法,能够解决实验过程中光源偏振性和孪生像对原子像的影响. 关键词： X射线荧光全息术 同步辐射 偏振性     

KB镜成像模拟以及与菲涅耳波带板成像的比较

采用坐标变换方法自编光线追迹程序模拟了Kirkpatrick-Baez镜在X射线波段的掠入射成像,获得了视场、分辨率等结果.比较了给定参量条件下Kirkpatrick-Baez镜与菲涅耳波带板两种高分辨X射线成像的特性,给出两者各自适用范围.Kirkpatrick-Baez镜成像有比较高的系统效率,在视场中心的空间分辨能力可达0.71 μm,但偏离视场中心±200 μm,空间分辨能力显著下降至6 μm,适用于较小视场的成像.菲涅耳波带板成像不仅在视场中心可以实现0.39 μm的空间分辨能力,偏离视场中心达±13 mm,空间分辨能力也几乎不变,可实现大视场高分辨成像.     

Simple and robust digital holography for high-resolution imaging

Based on the point spread function of holographic system,the lateral resolution of digital holographic imaging system without any pre-magnification is studied.The expression of resolution limitation of holographic imaging system is thus presented.We investigate the possibilities to improve the lateral resolution.The simple experimental setup with an off-axis arrangement is built.By using a U.S.Air Force(USAF)test target as microscopic object,the recorded holograms are reconstructed digitally based on the principle of Fresnel diffraction.The lateral resolution of 2.76 μm without any pre-magnification is demonstrated experimentally,which matches the theoretical prediction well.     

Advances in synchrotron hard X-ray based imaging

Modern synchrotron radiation (SR) sources have dramatically fostered the use of SR-based X-ray imaging. The relevant information such as density, chemical composition, chemical states, structure, and crystallographic perfection is mapped in two, or, increasingly, in three dimensions. The development of nano-science requires pushing spatial resolution down towards the nanoscale.The present article describes a selection of hard X-ray imaging and microanalysis techniques that emerged over the last few years, by taking advantage of the flux and coherence of the SR beams, as well as exploiting the advances in X-ray optics and detectors, and the increased possibilities of computers (memory, speed). Examples are given to illustrate the opportunities associated with the use of these techniques, and a number of recent references are provided. To cite this article: J. Baruchel et al., C. R. Physique 9 (2008).     

北京同步辐射装置上的位相衬度成像

在北京同步辐射装置上首次用位相衬度成像方法对生物样品和复合材料进行研究,得到了非常清晰而精细的材料内部细观结构.其图像的清晰度和分辨率明显地优于吸收衬度成像 关键词： 位相衬度成像 相干光源 同步辐射硬X射线     

The projection approximation versus an exact solution for X-ray phase contrast imaging, with a plane wave scattered by a dielectric cylinder

We show that exact solutions for an X-ray plane wave scattered by a dielectric cylinder with radius large compared to the radiation wavelength, give almost the same intensity fringes as seen when using the projection approximation (PA) to simulate propagation based phase contrast imaging. The characteristic Argand plane Cornu spiral and hypocycloid from the complex wavefield beyond the cylinder was observed to agree with the PA simulations. Asymptotic approximations to the exact analytical solution simplify to the projection approximation at the centre of the cylinder. The projection approximation underestimates observed fringes at a propagation distance comparable with the cylinder radius, but converges to the exact solution at larger propagation distances. This demonstrates that the complex ray approach of the projection approximation is insufficient, in comparison to the exact approach, when the propagation distances are sufficiently small.     

Super-resolution imaging in digital holography by using dynamic grating with a spatial light modulator

A super-resolution imaging method using dynamic grating based on liquid-crystal spatial light modulator (SLM) is developed to improve the resolution of a digital holographic system. The one-dimensional amplitude cosine grating is loaded on the SLM, which is placed between the object and hologram plane in order to collect more high-frequency components towards CCD plane. The point spread function of the system is given to confirm the separation condition of reconstructed images for multiple diffraction orders. The simulation and experiments are carried out for a standard resolution test target as a sample, which confirms that the imaging resolution is improved from 55.7 μm to 31.3 μm compared with traditional lensless Fourier transform digital holography. The unique advantage of the proposed method is that the period of the grating can be programmably adjusted according to the separation condition.     

Computer simulation of Fresnel diffraction from rectangular apertures and obstacles using the Fresnel integrals approach

In this paper, we describe a new computer simulation technique of generating Fresnel diffraction images from rectangular apertures of arbitrary dimensions by using Fresnel integrals instead of the more common fast Fourier transform methods. The simulation can be performed in almost any PC using the software MATLAB. Diffraction images can be generated for any wavelength of light and for any aperture–screen and aperture-source distances. Images for rectangular obstacles can also be simulated. Details of the algorithm and program are presented, as well as the interesting insights than can be gained from using the program. Finally, it is shown that the simulated images reduce to the simple Fraunhofer diffraction patterns for certain limiting situations.     

基于激光驱动等离子体X光源的X射线相衬成像

为了诊断惯性约束聚变(ICF)内爆靶丸球壳的多层信息,在神光Ⅱ激光器上对激光驱动等离子体X光源的相衬成像进行了研究。利用神光Ⅱ第9路激光驱动平面Ti靶获得X光源,在10μm的针孔约束下作为次级点光源对样品成像,用X光胶片记录。成功地将相衬成像技术应用于ICF实验,综合考虑成像放大倍数、分辨力、成像衬度和抑制烧蚀碎片等因素,选择合适的实验条件,成功获得了清晰的双层内爆靶丸球壳结构,空间分辨力优于10μm。     

点源参考光数字全息的频谱和记录能力分析

基于最高空间频率分析法,对点源参考光数字全息的空间频谱进行了分析,得出了使空间频谱分离的条件。结合全息成像系统的分辨率,推导出了同时满足采样和再现像分离的记录条件以及CCD对被记录物体的数据记录能力。结果表明,对给定的物体和CCD来说,采用点源参考光比采用平面参考光更容易满足采样和分离的条件,并可以记录到更多的物体信息,从而可使再现像获得更高的分辨率。