共查询到20条相似文献,搜索用时 51 毫秒
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在基于光栅的X射线相衬信号的恢复方法中,主要有相移法和傅里叶变换法两种方法.相移法具有精度高、噪声小的优点,但由于至少需要三幅图像才能恢复出相衬信号,样品所受的辐射剂量大.而傅里叶变换法只需一幅图像即可恢复出物体的相衬信号,具有快速、实时的优点,但恢复出的信号精度低,易受伪影影响.因此,本文利用两幅图像傅里叶变换法恢复X射线相衬信号,该方法能够有效地抑制相衬信号中由于频谱混叠所产生的伪影.另外,通过增加载波条纹的频率,能够拉大频域中的频谱间隔,从而进一步抑制伪影的产生. 相似文献
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泽尔尼克与相衬显微镜 总被引:3,自引:1,他引:2
相衬法是通过空间滤波器将物体的位相信息转换为相应的振幅信息,用改变频谱的位相来改善透明物体成像的反衬度,从而提高透明物体的可分辨性,泽尔尼克首先提出相衬法并发明了相衬显微镜.相衬显微镜现已在生物学、医学、晶体学、高分子材料结构性能的研究和矿物晶体微形貌学进行晶体表面生长的动态观察中获得了相当好的效果. 相似文献
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在所有的相衬成像方法中,X射线同轴轮廓成像由于光路简单、不需要任何光学元件而备受关注.其缺点是无法直接消除散射的影响,从而限制了它在生物医学等领域中的应用.利用数字模拟方法研究了引入散射前后轮廓像的质量随样品到探测器距离的变化情况.模拟结果表明直接轮廓成像存在一个最佳成像距离,因而无法通过改变样品到探测器距离来减小散射的影响.利用定量相衬成像不受成像距离限制的特点,研究了远距离成像时散射的影响.结果表明,样品到探测器的距离增大到一个临界值时,散射对重构像的影响可降到一个极值,此时成像质量得到了明显改善.
关键词:
散射
X射线同轴轮廓成像
定量相衬成像 相似文献
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波的核心是相位,驻波的关键是入射波与反射波的相位差,入射波和反射波相位随x、t变化的关系可用相位图(移动的斜线)表示,而相位差仅随x变化,也可用斜线表示,这样即可很方便地确定波节和波腹的位置。 相似文献
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本文采用双模晶体相场模型,计算了双模二维相图;模拟了形变诱导六角相向正方相转变过程的多级微结构演化,详细分析了位相差、形变方向对位错、晶界、晶体结构、新相形貌的影响规律.模拟结果表明:形变方向影响正方相晶核的形核位置和生长方向,拉伸时正方相优先在变形带上形核,垂直于形变方向长大,而压缩时正方相直接在位错和晶界的能量较高处形核,平行于形变方向长大;位相差对形变诱发晶界甄没过程有显著影响,体现在能量峰上为,小位相差晶界位错的攀滑移和甄没形成一个能量峰,大位相差晶界位错攀滑移和甄没因分阶段完成而不出现明显的能量峰;形变诱导相变过程中各种因素相互作用复杂,是相变与动态再结晶的复合转变. 相似文献
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Chi Ching Chang 《Optical Review》1997,4(5):556-560
We demonstrate the simultaneous phase conjugation of multiple beams incident on the a face of a photorefractive barium titanate crystal. The input beam power, angle and position were set so that no phase conjugation occurs unless a switchable incoherent inducing beam is present on the — c face of the crystal. The use of the inducing technique with two mutually pumped phase conjugations for four input beams, or one self-pumped and one mutually pumped phase conjugation for three input beams can be performed in a crystal. Unlike the setup of conventional phase conjugation, which requires more precise arrangements, the novel setup of the multi-beam induced phase conjugation is relatively relaxed. The mechanism responsible for our discovery is qualitatively explained, and possible applications are mentioned. 相似文献
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In this work, our investigation is to study the optical and thermal properties of the binary mixture of cholesteric and nematic compounds, namely, cholesteryl nonanoate and p-methoxybenzylidene-p-ethylaniline, which exhibits a very interesting liquid crystalline twisted grain boundary (TGB) phase and reentrant smectic-A phase. The chiral liquid crystalline TGB phases and reentrant smectic-A phases have been observed at different concentrations and at different temperatures. The existence of TGB and reentrant smectic-A phases is confirmed by differential scanning calorimetry and optical microscopic studies. The variation of optical anisotropy has been discussed. The helical pitch of the cholesteric phase has also been discussed. 相似文献
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双频相位测量轮廓术及其误差分析 总被引:4,自引:0,他引:4
提出一种双频相位测量轮廓术,利用这一技术。在相位恢复过程中,对有断点及边界区域也能得到正确的去包裹相位值,把这一技术用于三维面形测量中,得到了较好的实验结果。最后,分析实验产生误差的原因。 相似文献
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We use the quantum kinematic approach to revisit geometric phases associated with polarizing processes of a monochromatic light wave. We give the expressions of geometric phases for any, unitary or non-unitary, cyclic or non-cyclic transformations of the light wave state. Contrarily to the usually considered case of absorbing polarizers, we found that a light wave passing through a polarizer may acquire in general a nonzero geometric phase. This geometric phase exists despite the fact that initial and final polarization states are in phase according to the Pancharatnam criterion and cannot be measured using interferometric superposition. Consequently, there is a difference between the Pancharatnam phase and the complete geometric phase acquired by a light wave passing through a polarizer. We illustrate our work with the particular example of total reflection based polarizers. 相似文献