Enhancement of sensitivity of measurements of the holographic lateral-shear interferometry in studies of fast processes

The possibility of enhancing the sensitivity of measurements upon visualization of temporal variations of a phase object by means of optical processing of the holographic lateral-shear interferograms, without the necessity of detecting the original holographic interferograms under nonlinear conditions, is considered. In rewriting the original holographic interferogram, it is advisable to change the orientation of the holographic fringes and to record the secondary holograms under nonlinear conditions. The proposed method for increasing the sensitivity of measurements was used to visualize variations of thickness of a polymethyl methacrylate plate in the course of its thermal treatment.     

光致聚合物全混洗光互连全息元件的制备

采用只对红光敏感的光致聚合物全息干版通过 Ｈｅ－Ｎｅ ６３２ｎｍ激光波长两次掩膜曝光,在面积为３０ｍｍ × ６０ｍｍ的全息干版上制备出全息光学元件,并成功地用于全混洗光学互连的实验演示。全息光学元件的衍射效率为 ４０～ ５２％。     

Diffraction efficiency and light-scattering power of photothermoplastic holographic gratings

The diffraction efficiency and light-scattering power of holographic gratings formed on the surface of a two-layer photothermoplastic carrier with a pit structure of deformation are studied. The influence of the height and regularity of the pit deformation on the diffraction efficiency and light-scattering power is studied. It is shown that the pronounced resonance character of the dependence of the diffraction efficiency on the spatial frequency in the case of pit deformation is related to the distribution of the deformation depth over spatial frequencies; however, the dominant factor is the mutual arrangement of pits within the interference fringe. It is found that the light-scattering power is determined for the most part by the size and density of the deformation. A new method is proposed for determining the resolution of photothermoplastic carriers with pit deformation, which apparently can be used for photothermoplastic carriers with any irregular structure of deformation. This method is based on the analysis of the dependence of the light-scattering power of holographic gratings on their spatial frequency. It is shown that the resolution depends inversely proportionally on the thickness of the thermoplastic layer of the optical carrier.     

On the feedback holographic associative memory

Theoretical expressions and convergence conditions are developed here for the output of a feedback holographic associative memory. It is shown that a feedback holographic associative memory becomes a pinhole holographic associative memory under certain conditions, and thus is a generalization of the pinhole holographic associative memory. The crosstalk in the output of a feedback holographic associative memory can also be removed by a threshold device or controlled by the overall optical efficiency of the memory. A simulation is provided to verify the theoretical results shown here. Using the theoretical results and simulation verification, a feedback holographic associative memory can be designed efficiently. In addition, if a threshold device is used, optical elements with high optical efficiency can be used in a feedback holographic associative memory.     

A method to accurately control the period of subwavelength planar holographic grating in the fabrication process of guided mode resonance filter

Subwavelength optical element such as guided-mode resonance filter has gained much interest recently due to its properties and applications. It is very hard to fabricate an ideal guided-mode resonance filter with the same parameters as the designed one. The reason is that the resonance wavelength of guided-mode resonance filter is susceptible to the fabrication errors of its parameters, such as the period, the groove depth, the thickness of a guided-wave layer, and the refraction indexes of materials, etc. In this article, a method to accurately control the period of subwavelength planar holographic grating which was used as a sub-layer of the guided mode resonance filter is investigated. Results show that utilizing a convex lens placed in the exposure position can cause the adjusting of the period of subwavelength planar grating more convenient in the holographic optical path during the fabrication process. Accuracy controlling the period of grating which was used as the sub-layer of guided-mode resonance filter has great significance in the fabrication of guided-mode resonance filter.     

Anisotropic diffraction of stratified volume holographic grating in photorefractive media

We have studied the anisotropic diffraction properties of the stratified volume holographic gratings recorded in photorefractive media using the anisotropic coupled wave theory. It is shown that the diffraction efficiency of such system exhibit the uniform periodic Bragg selectivity properties. In addition the dependence of the stratified volume holographic optical elements (SVHOEs) diffraction properties on the buffer-layer thickness, grating-layer thickness, number of modulation layers, and total thickness of system are discussed in detail.     

Characterization of electrodeposited Bi2S3 thin films by holographic interferometry

Optical non destructive evaluation methods, using lasers as the object illumination source, include holographic interferometry. It is widely used to measure stress, strain, and vibration in engineering structures. Double exposure holographic interferometry (DEHI) technique is used to determine thickness and stress of electrodeposited bismuth trisulphide (Bi₂S₃) thin films for various deposition times. The same is tested for other concentration of the precursors. It is observed that, increase in deposition time, increases thickness of thin film but decreases stress to the substrate. The structural, optical and surface wettability properties of the as deposited films have been studied using X-ray diffraction (XRD), optical absorption and contact angle measurement, respectively. The X-ray diffraction study reveals that the films are polycrystalline with orthorhombic crystal structure. Optical absorption study shows the presence of direct transition with band bap 1.78 eV. The water contact angle measurement shows hydrophobic nature of Bi₂S₃ thin film surface.     

制造全息光栅的新装置

本文报道一种利用洛埃镜原理制造全息光栅的新装置及其调整方法.该装置具有光学系统简单,干涉条纹定位精度高和调整方便等优点,可制造性能良好的全息光栅.     

莫尔条纹分析在数字全息存储器中的应用

针对像素不匹配的数字全息存储器中出现的莫尔条纹现象,提出了利用莫尔条纹进行全息存储光路精确调整来实现像素匹配的方法.通过对CCD像面图像中莫尔条纹的周期和角度进行分析,得到光学系统需要的精确调整参数.实验中,实现了空间光调制器和光电耦合器阵列512×512像素的1:1像素匹配,该方法能提高读取速度并降低误码率.     

莫尔条纹分析在数字全息存储器中的应用

针对像素不匹配的数字全息存储器中出现的莫尔条纹现象,提出了利用莫尔条纹进行全息存储光路精确调整来实现像素匹配的方法.通过对CCD像面图像中莫尔条纹的周期和角度进行分析,得到光学系统需要的精确调整参数.实验中, 实现了空间光调制器和光电耦合器阵列512×512像素的1∶1像素匹配,该方法能提高读取速度并降低误码率.     

A method for increasing the sensitivity of determination of the wavefront distortion in optical processing of holographic lateral shear interferograms

A method for obtaining interference patterns of increased sensitivity in optical processing of holographic lateral shear interferograms recorded under linear conditions at a shear exceeding the size of a phase object under study is proposed. Cases of reconstruction of interference patterns of increased sensitivity using matched and optically conjugate holographic lateral shear interferograms are considered. It is shown that two-and fourfold increases in sensitivity, respectively, are obtained in these cases. The validity of the method proposed is confirmed experimentally     

Realization of an optical interferometer based on holographic optics for real-time testing of phase objects

The paper describes a simple and cost effective method for the realization of an optical interferometer based on holographic optics, which use minimal bulk optical components. The optical arrangement in the proposed method involves a very simple alignment procedure and inexpensive holographic recording material is used in the formation of holographic optical elements. The proposed interferometer set-up is quite suitable for performing optical test studies on phase (transparent) objects in real-time. Recording schemes for the formation of holographic optical elements and the related technique for the realization of the interferometer set-up along with the experimental results have been presented.     

Holographic optics-based interferometer for real-time testing of phase objects

A simple and cost effective method for making holographic optics-based interferometer, which is suitable for performing optical test studies on phase (transparent) objects in real-time, has been described. The optical arrangement in the proposed method involves a very simple alignment procedure and inexpensive holographic recording material is used in the formation of holographic optical elements. Recording schemes for the formation of holographic optical elements and the related techniques for the realisation of the proposed interferometer along with typical experimental results have been presented.     

球面波照明下利用阿贝滤波制作全息光栅

在阿贝成像理论基础上,提出了一种球面波照明方式下的阿贝滤波制作全息光栅方法。该方法所用光学元件较少,光路简单易排,很容易制作出需要的低频光栅。     

数字全息成像技术测量侧边抛磨光纤包层剩余厚度

测量侧边抛磨光纤（side polished fiber,SPF）的包层剩余厚度对其应用有重要的指导意义,现今的测量方法均有所不足,现提出一种基于数字全息技术的测量方法。利用单模光纤纤芯折射率比包层折射率高的特点,基于数字全息成像技术,通过角谱传播法对二维全息图进行相位重构,并通过精确最小二乘法解相位包裹,得到侧边抛磨光纤的相位分布图。根据重构的相位分布图,进一步运用相关的边缘提取算法处理得到侧边抛磨光纤包层剩余厚度。实验测量结果与电子扫描电镜（SEM）测量结果相比,测量相对误差小于0.5%。这种测量方法是一种直接测量方法,减小了间接测量法中由于光纤不对称以及SPF轮廓边缘衍射所带来的测量误差,为侧边抛磨光纤包层剩余厚度的无损、在线测量提供了一种新的途径。同时,此方法还可应用于测量其他特种光纤,例如光子晶体光纤、微纳光纤等。     

A Color Holographic Reconstruction System by Time Division Multiplexing with Reference Lights of Laser

3D-TV systems by holography technique have been studied in the world. In this paper, we report a color holographic reconstruction system by time division multiplexing method with reference lights of laser. The method can reconstruct a color holographic image by switching reference lights of red, green and blue colors at certain intervals. We can observe a color holographic image using red and green lasers as the reference lights, a high minute liquid crystal display (LCD) panel as a spatial light modulator (SLM) and electro-shutters as the shuttering device of the laser lights in the optical system. This approach has some advantages. Namely, the structure of the optical system can be simple and the number of LCD panels in the optical system can be decreased.     

利用单个全息透镜实现光学变换的理论

在离散取样情形下,证明了利用单个全息透镜所组成的光学系统能够实现任意给定的线性变换;给出了为实现给定变换而设计全息透镜振幅和相位分布的方法;并以三种不同序的八维Walsh变换为例,得到了实现这些变换的全息透镜的振幅和相位分布。 关键词：     

Measurement of properties of silver telluride thin films using holography

Holography is an interferometric method of recording the light waves diffracted by a subject illuminated with coherent light. Holographic interferometry (H.I.) is one of the most important applications of holography. It is concerned with the formation and interpretation of fringe patterns, which appears when a wave generated at some earlier time and stored in a hologram is later reconstructed by interfering with comparison wave. We report a technique, which uses double exposure holographic interferometry together with simple mathematical interpretation, which allow immediate finding of stress and thickness of thin film. We tested the same for different normalities of solutions. It was further noticed that the fringe spacing changes with solution concentration as well as time of deposition. The thin films are prepared using electrodeposition technique. It’s structural, morphological and optical study carried out by XRD, SEM, and UV-Vis-NIR spectrophotometer.     

雾化场光学全息与数字全息联合测量

针对雾化场光学全息测量存在干板湿化学处理繁琐、再现像采集耗时的问题,提出光学全息与数字全息联合测量的方法,建立由同轴光学全息、同轴数字全息以及数字延迟信号发生器组成的测量系统,并以双孔直射式喷嘴产生的雾化场为测量对象,利用该测量系统在一次测量中同时获得雾化场的光学全息和数字全息的再现图像,两者具有很好的一致性。光学和数字再现图像相对应的视场范围分别为27.87 mm4.77 mm和27.59 mm6.67 mm,数字方式获得视场范围内单一层面再现像的时间仅为8 s,而光学方式将近1 h。结果表明,光学全息与数字全息联合测量时,通过数字全息的雾化再现图像能够对实验总体效果进行实时评估,提高了雾化场全息测量的实验效率。     

New photopolymerizable holographic recording material based on polyvinylalcohol and 2-hydroxiethylmethacrylate (HEMA)

We have developed a new polyvinylalcohol-based photopolymeric holographic recording material. The recording is obtained by the copolymerization of acrylamide and 2-hydroxiethylmethacrylate (HEMA). Diffraction efficiencies near 70% are obtained with exposures of ≈65 mJ/cm² in materials of 110-μm thickness. The addition of HEMA increases the thickness of the film, which results in improved storage capacity for holographic optical storage. Received: 7 March 2002 / Published online: 2 May 2002