A theoretical study on the visibility of a speckle pattern based on a Gabor hologram and speckle photography

The visibility of the speckle pattern resulting from the scattered radiation of transmitted beams through a diffusing surface has been studied for a Gabor hologram and speckle photography. The cases of strictly- and quasi-monochromatic light are also considered. Mathematical expressions for the dependence of the visibility on the distance from the centre of the undiffracted illuminating beam, its spectral half-width Δf and the amplitude ratio m between the reference beam and the integrated scattered beams are obtained. A graphical method is found for determining m and Δf from the visibility as a function of the distance from the centre of the undiffracted illuminating beam.     

A new theta modulation multiplexing scheme for computer-generated holograms

In this paper, a new theta modulation multiplexing scheme for producing multiplexed computer-generated holograms (CGHs) is proposed. Under this scheme, normal Lohmann-type CGHs are individually modulated by gratings with different orientations and then superimposed to form a single hologram. The proposed method results in a higher storage capacity without the increase of hologram space. Theoretical analysis and experimental results are presented.     

A strong adaptable autofocusing approach of off-axis infrared digital holography under different quality conditions of holograms

In this paper, we present an innovative autofocusing criterion for the reconstruction of infrared digital holograms. This criterion has the advantages of fast, efficient and precision when determining the reconstruction distance of off-axis digital holography. This criterion is a mean-free high frequency calculation process. We focus on the problem of mean value drifting found in previous published methods and design our new approach to solve it. Unlike the previous methods perform well only with high quality holograms, our method is effective for both high and low quality holograms. Even when hologram is degraded by destructive interference, our method still performs well. This method helps to automatically determine the precise reconstruction distance, and we are sure that this technology can be applied in industrial applications in the future.     

One-step, full-view rainbow holograms with conventional plates of 6 μm emulsion

A method of one-step full-view rainbow holography using conventional holographic plates of 6 °m emulsion as recording materials is described aand experimentally demonstrated. The requirement for the inter-beam angle to avoid cross-talk between two images is discussed. The simplicity and low cost of this method make it particularly suitable for the full-view white light holographic display of moderate-sized objects.     

Wavelet processing and digital interferometric contrast to improve reconstructions from X‐ray Gabor holograms

In this work, the application of an undecimated wavelet transformation together with digital interferometric contrast to improve the resulting reconstructions in a digital hard X‐ray Gabor holographic microscope is shown. Specifically, the starlet transform is used together with digital Zernike contrast. With this contrast, the results show that only a small set of scales from the hologram are, in effect, useful, and it is possible to enhance the details of the reconstruction.     

伽柏与全息术的诞生

简述了伽柏为实现全息术所产生的“波前重建”的构想，并展示了激光全息术的广阔应用前景。     

Two-channel computer-generated holograms: a simplified method

A simplified approach is presented, to obtain two-channel computer-generated holograms of detour type. The method allows effectively to handle up to two flat objects (two digitized images), in x and ydirections. The experimental results demonstrate the effectiveness of the suggested procedure.     

Waveguide holograms: A new approach to hologram integration

A new class of holography is proposed, in which (1) the evanescent part of a guided wave, or (2) the guided wave in a thin-film hologram is utilized as the reference wave and/or the illuminating one. The hologram was designated as “wave-guide hologram” and has advantages in the possibility of integration, wide field of view, and compactness and high reliability of the reconstructing system. The possibility of the waveguide hologram has been proved through reconstruction experiments with a guided wave of a waveguide hologram recorded with a plane reference wave.     

Application of liquid crystal (LC) devices for optoelectronic reconstruction of digitally stored holograms

Recent advances in high-resolution CCD detectors allow the development of the concept of digital holography that relies on the capture of 2D microinterferograms and their further numerical reconstruction. This approach is valid for optical metrology applications as it gives direct access to the phase and intensity of an object at the selected distance “d”. However, it is not convienient for direct 3D-display purposes. This is the reason why the authors propose the optoelectronic reconstruction of a hologram that is digitally recorded and transferred to another optoelectronic medium. The application of LCD matrices and optically addressed liquid crystal cells as reconstruction media is discussed. Their applicability for computer-generated and optical holograms is tested by means of simple experiments. The problems connected with limited resolution of the recording (CCD) and reconstruction (LCD, DMD) devices are considered. The comparison of the results obtained by numerical and optoelectronic means is presented, together with a discussion of the limitations and further possibilities of these techniques.     

Mathematical method to predict the diffraction efficiency of holograms

In this paper, a method is presented which uses a multi-factorial decision model of fuzzy-set theory to predict the diffraction efficiency of holograms. A prediction fitting rate of 85% has been obtained. This method can be used as a guide to processing holograms.     

Reconstruction of holograms generated by using a combination of an iterative method and an error diffusion method

Two-level quantized phase holograms produced by using a combination of an iterative method and an error diffusion method are presented. By using a previously proposed iterative method, images reconstructed from two-level quantized phase holograms are rapidly improved with small amounts of iterative operations but further improvement of the image quality is difficult even if the iterations are greatly increased. Therefore, in order to exceed the improvement limitation of the image quality, the combination of the iterative method and an error diffusion method was used for the hologram-making process. Experimental results using the combination method showed better images than those obtained by the iterative method alone, when referred to results from synthesized holograms.     

提高重铬酸盐明胶全息图环境稳定性的一种新方法

在明胶水悬浮液中加入少量聚乙烯醇及必要的添加剂,经重铬酸铵敏化后曝光制作Lippmann全息图.实验表明,与用传统方法制作的重铬酸盐明胶全息图相比,其环境稳定性有了明显的提高,本文还讨论了聚乙烯醇等物质的加入所起的作用及这种全息图环境稳定性提高的机理.     

加窗傅里叶变换在三维形貌测量中的应用

采用加窗傅里叶变换技术(GTGM)对变形光栅图像进行分析在窗口区域内提取基频,并随着窗口的移动进行叠加,有效地重构出全部的基频信息,改善了不同频谱的叠加现象,提高测量的精度.     

伸缩窗口傅里叶变换在三维形貌测量中的应用

为了克服窗口傅里叶变换在分析非平稳信号所存在的缺陷,基于窗口傅里叶变换技术提出了伸缩傅里叶变换法并应用于三维形貌测量中。通过对窗函数在空间尺度上引入伸缩变换,得到一个可调宽度的空间一频率窗,实现空间频率分辨率随光栅图像条纹频率变化自动可调的实时快速测量。该方法克服了窗口傅里叶变换分析中所有频率窗口的大小形状固定不变的缺点,适合复杂物体形貌的测量。给出了理论分析、计算机模拟以及实验研究结果。     

Contouring of diffused objects by using digital holography

A simple method for contouring of diffused objects by using lensless Fourier transform digital holography (LFTDH) and dual-index immersion method is presented. Depth contour interval up to minimum of 0.12 mm could be achieved without making the interference phase fringes over crowded.     

Hyper-Raman microspectroscopy: a new approach to completing vibrational spectral and imaging information under a microscope

We have developed hyper-Raman scattering microspectroscopy and applied it to a microcrystal of all-trans-beta-carotene. The hyper-Raman spectrum of all-trans-beta-carotene exhibits a Raman-inactive but infrared-active vibrational mode at 1564 cm(-1). Hyper-Raman imaging of a microcrystal was performed with this band. Infrared-active vibrational imaging was achieved with a spatial resolution much higher than that of conventional infrared microscopy. The combination of Raman and hyper-Raman spectroscopy opens up a new scope for high-spatial-resolution vibrational microspectroscopy that is not restricted by the selection rule.     

Improved low energy electron projection in-line holograms reconstruction: application to the holograms of a tungsten tip

A modification of the classical calculation algorithm is presented which allows to minimize the effect of the long range oscillations created by the twin object in the reconstruction process of in-line holograms obtained by low energy electron projection microscopy. The reconstructed shapes of a tungsten tip, observed with different magnifications are shown.     

基于Fisher信息理论的突变检测新方法

自然界许多复杂系统的动力学结构因其受外强迫的作用, 常常会发生与人类生活密切相关的突变. 对突变做出准确预测并采取相应对策的有效途径就是检测. Fisher信息(FI)是一种能够敏锐捕捉并刻画系统变量的概率密度分布发生微小变化的量; 而当系统的动力学结构发生突变时, 来自突变前后两种不同动力学结构的数据其概率密度分布肯定会发生不同程度的改变. 基于此,本文将它用于检测和识别系统动力学结构所发生的突变, 以一种全新的思路来解决突变检测问题. 首先通过理想数据序列展示了使用FI来表征各种不同类型理想信号突变的能力. 进而应用于中国气象局国家气象信息中心“西北地区地面气候资料日值数据集”兰州站1960–2008年日平均气温资料的实际检测中, 结果表明与已有历史记载相符合, 进一步验证了该方法的有效性和实用性. 关键词： Fisher信息 动力学结构 突变检测 概率密度分布     

Soft annealing: a new approach to difficult computational problems

I propose a new method to study computationally difficult problems. I consider a new system, larger than the one I want to simulate. The original system is recovered by imposing constraints on the large system. I simulate the large system with the hard constraints replaced by soft constraints. I illustrate the method in the case of a ferromagnetic Ising model and in the case of a three-dimensional spin-glass model. I show that in both models the phases of the soft problem have the same properties as the phases of the original model and that the softened model belongs to the same universality class as the original one. I show that correlation times are much shorter in the larger soft constrained system and that it is computationally advantageous to study it instead of the original system. This method is quite general and can be applied to many other systems.