四方晶系SBN晶体中位错光双折射像的理论计算和实验观察

本文计算了铌酸锶钡(SBN)晶体中沿光轴的位错双折射像的反衬,计算中考虑了光弹系数的各向异性,结果表明与各向同性计算相比刃位错双折射像中的花瓣有伸长的趋势,螺位错无反衬,并与实验结果作了比较。     

应用反射光双折射貌相法观察旋光性晶体锗酸铋中的位错及亚晶界

本文对具有强旋光晶体锗酸铋(Bi₁₂GeO₂₀)进行了光双折射貌相的研究,发现采用反射偏光显微镜可以完全抵消晶体的自然旋光性并获得良好效果。观察了锗酸铋晶体中位错及亚晶界的双折射象。确定了位错的柏格斯矢量为1/2〈111〉,〈100〉及〈110〉。 关键词：     

六角片状包裹体双折射象与计算机模拟象

在钆镓石榴石(GGG)晶体中观察到六角片状大包裹体的应力双折射象,对其应变场进行了分析,并计算双折射象的反衬和作出相应的数值模拟象,实验与理论计算结果符合得较好。     

直拉法生长的GGG和YAG单晶体中螺型位错的双折射像

在直拉法生长的GGG和YAG单晶体中,从实验上首次获得了沿位错线观察的(viewed end-on)螺型位错的双折射像,确立了沿位错线观察和垂直于位错线观察(viewed from the side)的双折射像间的一一对应关系,以及与蚀斑间的一一对应关系,并基于石榴石晶体弹-光性质的各向异性,给出了沿位错线观察的螺型位错双折射像的成像规律,得到了理论与实验一致的结果。 关键词：     

位错在裂纹顶端的象力

本文利用保角变换方法计算了近椭圆孔边位错象力。将椭圆一轴缩小到零,得到了裂纹情况的位错象力。 关键词：     

裂纹顶端的异号位错和无位错区的象力理论

本文改进BCS型裂纹位错模型,并对裂纹顶端范性区的位错密度分布进行了计算。结果指出,在紧靠裂纹顶端的滑移面上出现和裂纹位错异号的位错。这些负号位错将移至裂纹顶端并使之钝化而留下一个无位错区或低位错密度区。本文对无位错区形成的象力理论进行了讨论。 关键词：     

在YAG:Nd晶体中位错对激光特性的影响

本文用双折射貌相法和化学腐蚀法测定了六根晶体棒中的位错分布和位错密度,用光学方法检验了晶体的光学质量,晶体的激光性能是在一台Q开关YAG激光装置上测定的。实验表明当位错密度增加到一定程度时,位错形成的应力场会引起明显的双折射,以致探测光通过晶体时波面会发生畸变。在干涉仪上可观察到干涉条纹的增加。同样,在位错应力场区消光比亦下降。因此,作为结构缺陷的位错也是晶体光学不均匀的来源之一。晶体激光性能的实验结果指出:位错对激光输出特性有很大的影响,从激光近场光斑图看出,在位错应力场区,因为高的激光阈值而不能产生激光振荡,并且由于应力双折射效应产生光的退偏性。由于存在高位错密度,晶体的激光发散度增加,倍频效率下降。当晶体中存在缀饰位错(decorated dislocation)时,激光输出特性的变化尤为明显.     

晶体中滑移的位错机构研究

在研究岩盐型晶体的塑性变形中,用偏振光方法观察晶体中在塑性变形时出现的双折射光带,并结合用显微干涉仪对晶体表面的研究,观察到晶体中发生滑移时滑移带两端所发生的滑移距离恆不相等。根据这一结果,用腐蚀方法观察晶体中的位错排列,并和双折射光带及表面干涉图形的研究对比,全面地验证了离子型晶体中滑移过程的位错机构。此外,还证明了腐蚀坑和位错之间的一一对应的关系,并用实验方法证明了晶体滑移面内存在着符号不同的位错。     

非均匀微结构光纤中双折射现象的研究

报道了利用飞秒脉冲激光与非均匀微结构光纤相互作用中产生超连续光谱后在非均匀微结构光纤传输中双折射拍频现象的研究.利用35?fs的飞秒激光脉冲在高双折射微结构光纤中的传输过程中直接观察到了拍频现象.并利用有限元方法对该光纤进行了模拟计算分析，计算得出在600?nm处拍频长度为毫米量级.所得结果与实验一致. 关键词： 双折射效应 微结构光纤 超连续光谱 有限元法     

直拉法生长Y_3Al_5O_(12)(YAG)单晶体中的位错和包裹物

通过光双折射貌相法研究了YAG单晶体中位错、包裹物以及生长层间的关系,结果表明,包裹物优先吸附于固液界面上的位错露头点,而包裹物的大小与该处生长台阶的大小有关。     

光学相干层析图像层状结构的增强与定量测量

光学相干层析(OCT)成像技术对于眼底等层状组织的定量测量有赖于光学相干层析图像中层状结构的提取。为了对原始光学相干层析图像进行预处理以有效地去除图像中的噪声及散斑、增强图中的层状结构,并更好地保护图像中的层状结构,进而更准确地定量测量图像中有重要意义的层状结构的光程信息,提出在相干增强各向异性扩散(CED)算法中引入二阶导数项以控制沿相干方向的扩散强度,并将引入二阶导数项的相干增强各向异性扩散算法应用于不同样品的光学相干层析图像。结合在预处理后图像中层状结构位置的查找结果与样品的折射率信息,实现了对光学相干层析图像中有重要意义的层状结构厚度的定量测量。实验结果表明,使用引入二阶导数项的相干增强各向异性扩散算法对光学相干层析图像预处理有利于对图中重要层状结构的更准确测量。     

Comparative analysis of the resolving power of optoelectronic imaging systems upon incoherent and coherent illumination of objects

Results of calculations of the resolving power (according to Foucault) of optoelectronic imaging systems with incoherent and coherent illumination under the conditions of atmospheric phase distortions are presented. It is suggested that incoherent optical images are formed in the case of incoherent illumination and speckle images are formed in the case of coherent illumination. The shape of objects observed is estimated from these images. The resolving powers are shown to be practically the same in the formation of incoherent optical images and speckle images in the case of strong phase distortions and smoothing of images by a matrix photodetector. At the same time, the limiting resolving power in the formation of incoherent optical images is twice as large as in the formation of speckle images.     

最近邻域与无邻域算法结合空间滤波实现显微光切片

运用最近邻域与无邻域算法,并结合空间滤波方法,可去除显微切层图像的离焦模糊成份,可获得高成像速度、高质量的显微光切片。对各种显微图像进行了光切片处理,并与由现有去卷积处理、结构光照明等方法获得的光切片图像进行了对比,验证了该算法在去除模糊信息方面有更好的效果,提高了图像处理效率,获得了令人满意的光切片图像。在此基础上研制出了显微光切片图像处理系统。运用最近邻与无最近邻算法,结合空间滤波方法,采用简便可调的卷积模糊算子代替点扩散函数的估计过程,图像处理方便快捷,可较好地去除离焦平面的模糊信息。     

Simultaneous parametric generation and up-conversion of entangled optical images

A quantum theory of parametric amplification and frequency conversion of an optical image in coupled nonlinear optical processes that include one parametric amplification process at high-frequency pumping and two up-conversion processes in the same pump field is developed. The field momentum operator that takes into account the diffraction and group velocities of the waves is used to derive the quantum equations related to the spatial dynamics of the images during the interaction. An optical scheme for the amplification and conversion of a close image is considered. The mean photon number density and signal-to-noise ratio are calculated in the fixed-pump-field approximation for images at various frequencies. It has been established that the signal-to-noise ratio decreases with increasing interaction length in the amplified image and increases in the images at the generated frequencies, tending to asymptotic values for all interacting waves. The variance of the difference of the numbers of photons is calculated for various pairs of frequencies. The quantum entanglement of the optical images formed in a high-frequency pump field is shown to be converted to higher frequencies during the generation of sum frequencies. Thus, two pairs of entangled optical images are produced in the process considered.     

Near-field optical microscope with a multiheight scanning imaging mode

A near-field scanning optical microscope has been developed to yield optical images with various gap distances between the probe and the sample surface. The microscope uses an apertureless metallic probe, the position of which is controlled by regulation of the tunneling-electron current from the probe to the sample and by computer-generated bias voltage. Experimental results of near-field optical imaging with the developed microscope at different gap distances are shown. Thirteen images at gap distances of 0 to 500nm demonstrate that the near-field image depends strongly on the gap distance. The imaging characteristics of a near-field imaging system are shown with the spatial-frequency spectra of images. Future investigation of the developed microscope is also discussed.     

Compact, reliable asymmetric optical configuration for cost-effective fabrication of multiplex dot matrix hologram in anti-counterfeiting applications

This study presents a compact optical configuration that can generate a multiplex dot-matrix hologram with complex interlaced images for anti-counterfeiting applications on valuable paper. Varying the orientation of the interference plane can enable the multiplex hologram to be recorded without changing the interference angle of two laser beams. With its simple asymmetric optical setup, a multiplex hologram with many interlaced images can be efficiently fabricated, increasing the cost of imitation. Experimental details of the asymmetric optical setup are also described.     

Strain and vibration analysis by fibre based speckle shearing interferometry

An optical fibre based, speckle shearing interferometer is described. The instrument uses a highly birefringent optical fibre to illuminate a test object with equal intensities of light guided by the orthogonal polarisation eigenstates of the fibre. A Wollaston prism is used to obtain two sheared images with adjustable shear. Optical phase changes between the sheared images are readily achieved, without mechanical movement of components, by straining the optical fibre. Object strain determination, by fringe analysis with phase stepping techniques, is readily achieved. Vibration analysis by heterodyning is also reported.     

基于局部光流约束的角点匹配算法

提出了一种基于局部光流约束的角点匹配算法。首先采用Harris算子获得当前帧和参考帧的角点,然后以角点的光流特征作为约束条件,根据两帧图像角点集的坐标分布,排除异常角点,完成角点的精确匹配,实现图像之间的高精度运动估计。通过对视频序列进行实验,采用差图法可主观地发现该运动估计算法的有效性;以峰值信噪比作为评价指标,发现原始视频序列的帧间峰值信噪比明显低于仿射视频序列的帧间峰值信噪比。前者的平均值为22.8072,后者的平均值为33.3854,从而客观地说明了该算法的有效性和稳定性。     

Flexible optical encryption with multiple users and multiple security levels

We present a basic optical encryption architecture that admits several cryptography applications based on multiplexing. Users can decrypt different private images from the same encrypted image, a superuser can have a key that decrypts all encrypted images, and multiplexed images can be encrypted with different levels of security. This system is presented in the context of a general framework of optical encryption application development. We illustrate with a real-world three-dimensional scene, captured with digital holography, and encrypted using the fractional Fourier transform, where different users have access to different three-dimensional objects in the scene.     

Differentiation of Pigmented Skin Lesions Based on Digital Processing of Optical Images

Optics and Spectroscopy - A method for differentiation of pigmented skin lesions is proposed that is based on digital processing of optical images. The optical images are detected using a digital...