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题名	台式激光等离子体X射线源的全息显微研究
作者	张长学
学位类别	硕士
答辩日期	2001
授予单位	中国科学院上海光学精密机械研究所
导师	韩申生
关键词	X射线 全息显微 部分相干 台式
中文摘要	成像系统所能达到的极限分辨率受制于成像所用的波长，X射线波长很短的特性使以这种射线作为成像光源的成像方式有达到纳米量级分辨率的可能性。X射线在显微成像技术领域的应用有很突出的优点，与可见光及电子束相比，X射线具有很强的穿透性，在某些情况下成像物体对X射线而言几乎是完全透明的，此时用全息成像方法记录X光的相位变化，有可能对厚样品的内部结构进行无损探测，这是其它成像方式所无法做到的。由于以上优点，X射线的全息成像研究一直非常活跃。目前此类实验多采用大型同步辐射装置作为X光源对薄样品成像，并用数字方法复原原物体。另外，国内外在利用激光与固体靶相互作用产生X射线及其应用方面也进行过很多尝试，但将这种台式X射线源用于全息成像实验中的研究才刚刚起步。本文从实际的实验条件出发，系统研究了利用台式激光等离子体X射线源进行全息显微成像实验并获得有实际意义的成像结果的实现方法，主要包括以下几个方面的内容：1．激光等离子体X射线全息显微成像的模拟实验从理论上分析了目前实际可获得的台式激光等离子体X射线光源的各项性能指标，论证了利用这类设备获得有实际应用价值的X光全息图的可行性。并在此基础上编制出模拟同轴全息成像及图像复原的软件并进行模拟实验，探讨了包括X射线的相干性、信噪比、光源强度和记录距离等各种参数对实验结果的影响。与同步辐射装置相比，激光等离子体X射线源产生的X射线具有不同的物理特性。它的光源强度较低，时间和空间相干性也差一些。我们采用改进的实验光路和优化的复原算法，以期得到理想的实验结果。另外还研究了缩短曝光时间及获得更高分辨率的可能途径，讨论了其它几种对成像结果可能产生影响的因素。2．部分相干X射线同轴全息数字复原时干扰衍射斑的消除同轴Gabor全息实验中数字复原时除原物体的复原像外总会出现一些干扰衍射斑。它们在复原面上与物体复原像相瓦叠加，使成像质量下降。目前应用在X射线全息实验中的光源，特别是台式X射线全息实验可望使用的激光等离子体X射线源，都有两个明显特点：1．成像光束为部分相干2．光源强度不高。为解决这些问题，我们必须尽量减小成像时的记录距离，而这会使干扰衍射斑的问题变得更加严重。针对此类光源的特点，探讨了用参考光的共轭光束复原时像面上将出现的0级和+1级的衍射光斑的成因，在部分相干光照明情况下数字复原时分别提出解决方法。归纳了不同光路尺度下全息复原的一般规律，并提出某些情况下可能用到的其它几种改善复原像的途径。作者还首次提出了一种有待理论和实验验证的虚拟透镜法消除孪生像的设想。3．台式激光等离子体X射线源的设计已经进行的激光与各种靶材相互作用产生X射线辐射的实验并不少，但针对作为X射线全息实验光源的特点的分析却还不多。实现台式X光光源上的全息显微成像实验，关键问题是研制出性能稳定，能达到一定输出强度和相干度的光源。结合全息实验对光源的要求和固体靶X射线辐射特性，我们详细描述了台式X光光源的一种设计方案及工作过程，计算了它的各项性能指标。介绍了该装置的优越性，并对如何提高光源性能作了进一步的探讨。总之，为了发展小型化X射线源，利用台式装置进行能达到一定成像质量的全息成像，作者对部分相干照明条件下的X射线全息显微成像作了系统的研究，从理论上为这类实验作了准备，编制了能研究全息实验的记录和复原过程的软件，并提出利用图像处理技术改善成像质量的较为成熟的方法。在此基础上设计出利用固体移动靶的台式激光等离子体X射线源，为进一步的实验和理论工作作了充分的准备。
英文摘要	The ultimate image resolution is determined by wavelength of the image light. Wavelength of x-ray is very short and then it' s possible to get resolutions of several nm by this kind of image method. X-ray has showed many notable advantages when used in the field of microscopic imaging technology. X-ray has powerful penetrability compared with electron beam and visible light. Under special conditions objects are nearly lucid to x-ray and their shift of phase can be recorded by holography. So it's possible to detect the internal structure of thick objects without damaging them. This can' t be replaced by any other image method. For the advantaged showed above, researches on x-ray holography have been very active for years. At present large-scale synchrotron light sources are widely used in these kinds of experiments and the holograms are often reconstructed numerically. On the other hand, scientists all over the world have done experiments to get x-ray from interaction of laser and plasma and studied on its usage, but researches on using this kind of table-top x-ray source into holographic imaging experiment are only about to start. From actual experimental level, to employ table-top laser-plasma x-ray source into holographic microscopy is studied systematically including these contents: Simulative experiment on laser-plasma x-ray holographic microscopy Different property parameters of practically available table-top laser-plasma x-ray source are analyzed theoretically, and the feasibility of getting valuable x-ray hologram using these kinds of facilities is proved. On the basis of these achievements we program and simulate in-line holography and image reconstruction. Parameters including x-ray coherence, signal to noise ratio, source intensity and recording length that can influence experimental result are discussed. Laser-plasma x-ray sources have different physical characters compared with synchrotron sources. They have relative low light intensity and worse coherence. We employ improved experimental setup and ameliorative reconstruct algorithm to get good experiment result. Furthermore, we have studied possible methods to reduce exposure time and to acquire higher resolution. Some other characters that may influence the image result are also discussed. Elimination of disturbing diffraction in partially coherent x-ray table-top inline holography experiment There will always appear some disturbing diffraction faculas except the real image in the reconstruction of in-line Gabor holography. They interfere on the reconstructed plane and damage the image resolution. The current x-ray sources used in holography experiments, especially laser-plasma x-ray sources which can be used in table-top x-ray holography, have two evident characters: 1. light beam is partially coherent and 2. the source intensity is not very high. To resolve these problems, we must reduce the length between specimen and recording medium, which will make the influences of disturbing iffraction more serious. In accordance with characteristics of these sources, we studied the causations of 0 and +1 grade diffraction faculas that will appear on image plane when reconstructed by conjugate light beam of image light. Solutions of eliminating them are presented respectively when imaged by partially coherent x-ray. Some other possible solutions for enhancing the image quality that can be employed in some special conditions are discussed as well. For the first time, we present a scheme using virtual lens to eliminate twin-image that need to be verified. Designation of table-top laser-plasma x-ray source There have been many experiments that tried to generate x-ray radiation from interaction of laser and different kinds of targets. To do holographic microscopy experiments on table-top x-ray source, the key problem we must resolve is to make stable source with proper output intensity and coherent degree. Considering requirements of exposure and properties of x-ray generated from solid target, we describe scheme and work pattern of a kind of table-top x-ray source in detail, and compute performance norm of it. The advantages of this kind of source are introduced. We also discuss how to improve its performance. In short, to develop minitype x-ray source and do holographic image experiments with proper resolution, we have studied systematically on x-ray microscopic holography that' s illuminated by partially coherent light prepare for it theoretically. We have worked out programs to simulate recording and reconstruction of holography experiment, and presented pretty mature digital signal process method to improve image quality. Based on these theoretical researched, we designed a kind of laser-plasma x-ray source employing moving solid target. We wish it could do good to our further theoretical and experimental study.
语种	中文
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/16473]
专题	上海光学精密机械研究所_学位论文
推荐引用方式 GB/T 7714	张长学. 台式激光等离子体X射线源的全息显微研究[D]. 中国科学院上海光学精密机械研究所. 2001.

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