极弱散射结构中的随机激光器

提出了一种基于空间散斑的极弱散射随机激光系统,并用该系统在不同抽运条件下分别实现了相干反馈输出和非相干反馈输出.结果表明,两种反馈机制存在内在的联系.提出了随机腔耦合的概念,对弱散射随机激光器的模式特性给出了合理的解释.     

基于波导、金和氧化锌的随机激光器的研究

通过将金属金嵌入到上下两层波导结构中,与ZnO随机粒子相结合,设计出一种新型结构的随机激光器。采用时域有限差分法(FDTD),数值模拟了该随机激光器系统的光场分布和模式频谱图,并针对金粒子和金薄膜两种情况进行对比分析。结果显示,采用金粒子作夹层时,出射激光模式数量减少,单色性较好;采用金薄膜作夹层时,出射激光光强较大。     

Conjugate Image Plane Correlator with Holographic Disk Memory

A conjugate image plane correlator with holographic disk memory is proposed. Optical correlation between conjugate images reconstructed from a holographic disk and an input image on liquid-crystal television is executed with the rotation of the disk. Regardless of Fourier hologram recording with the pseudorandom diffuser, it is found possible to take out the diffuser from the original hologram recording scheme using an image reconstruction process and to get correlation signals between input and reconstructed conjugate images in the output plane of a two-lens imaging system. Generation of conjugate replicas with high contrast causes exact matching with an input image which results in high recognition performance for autocorrelation signals. The transfer function of an optical system can be controlled by adjustment of either hologram size or hologram area illuminated with a laser beam. Hence, the output intensity distribution can be adjusted by selecting a proper pupil function and the size of an output pupil defined by the input pupil size and the optical system magnification factor. The real-time character recognition by optical parallel high-speed processing for two dimensional images with position normalization is demonstrated.     

数字全息显微系统结构参量对再现像质的影响

为了获取高质量的数字全息显微再现像,分析了同轴相移数字全息显微系统结构参量对再现像质的影响.首先经过计算得出理想成像时,像空间物光波频率完全由物体面形结构频率和系统放大倍率决定.然后基于显微成像时物光波的所有频率分量都应该被有效记录的分析,得出在同轴相移系统中放大倍率必须使物光波的空间频率缩小到满足采样要求|并得出在相同的放大倍率下记录距离会影响有效记录的物体尺寸,记录器件离开像平面的距离越小,有效记录的物体尺寸越大,在像平面上时有效记录的物体尺寸最大.计算机仿真和光学实验都证明了上述结论的正确性.     

图像的全息描述与编码

图像在不可靠信道中传输时由于信道误码和数据丢包等因素的干扰,解码图像的质量会受到很大的影响。图像的全息描述和编码能够很好地用于图像的鲁棒传输。对一维和二维全息描述进行了分析,给出了全息描述的数学表达,把基于小波变换域的图像编码方法用于图像的全息描述。对该方法进行了测试,结果表明该方法具有较好的抗误码特性。     

Holographic visualization of flaws using magnetic stressing

A method of magnetic stressing is described. The results of holographic non-destructive testing using magnetic stressing are also reported.     

Image Security Based on Three-Dimensional Chaotic System and Random Dynamic Selection

Image encryption based on a chaos system can effectively protect the privacy of digital images. It is said that a 3D chaotic system has a larger parameter range, better unpredictability and more complex behavior compared to low-dimension chaotic systems. Motivated by this fact, we propose a new image cryptosystem that makes use of a 3D chaotic system. There are three main steps in our scheme. In the first step, the chaotic system uses the hash value of the plaintext image to generate three sequences. In step two, one of the sequences is used to dynamically select confusion and diffusion methods, where confusion and diffusion have three algorithms, respectively, and will produce 3²ⁿ (n > 100) combinations for encryption. In step three, the image is divided into hundreds of overlapping subblocks, along with the other two sequences, and each block is encrypted in the confusion and diffusion process. Information entropy, NPCR, UACI results and various security analysis results show that the algorithm has a better security performance than existing, similar algorithms, and can better resist clipping, noise, statistical analysis and other attacks.     

Shockwave Visualization Using Holographic Interferometer

High-speed holographic interferometry was employed to visualize and record Shockwave phenomena. We performed three kinds of holographic interferometry for visualization and recording of the propagation of a Shockwave: a real-time holographic interferometer with a high-speed framing camera, a real-time holographic interferometer with a high-speed streak camera and a double-pulse laser holographic interferometer with a dual-reference-beam module. The experimental results were compared and their advantages and disadvantages are discussed. The experimental results clearly show the high-speed Shockwave propagation and give the feasibility of quantitative interpretation of high-speed gas-dynamics.     

Holographic digital data storage using phase-modulated pixels

We propose and demonstrate the use of phase images for holographic data storage. Use of phase images as input leads to uniform diffraction efficiency of multiplexed data pages. Use of binary phase-based data pages with 0 and π phase changes produces uniform spectral distribution at the Fourier plane. This in turn facilitates better recording of higher spatial frequencies. We experimentally demonstrate a phase-based holographic data storage system using shift multiplexing in a Fe:LiNbO₃ crystal, and use it for associative retrieval. Preliminary studies indicate high discrimination capabilities of phase-based holographic data storage system over the amplitude-based system in a content-addressable memory.     

基于双随机相位编码的彩色图像加密技术

为了实现仅用两个密钥对彩色图像进行加密,提出了一种基于光栅调制的彩色图像加密方法.该方法首先把彩色图像分成三基色分量:红,绿,兰.然后,把这三帧灰度图像分别用空间频率不同正弦振幅光栅调制,之后,再把调制结果进行叠加而形成一个实值目标图像,该目标图像包含了原始彩色图像的全部信息.对此目标图像进行双随机相位加密系统的加密,即实现了彩色图像的加密隐藏.由于正弦光栅的调制作用,R、G、B灰度图像的频谱在实值目标图像的频谱中分离开来,通过选取合适的滤波窗口,就可以对他们的频谱分别提取并予以重建,并最终实现重构原始彩色图像.本文给出了理论分析和计算机模拟,实验结果证实了该方法的可行性.     

纳米随机激光

介绍了以纳米ZnO粉末作为增益介质产生的随机激光。讲述了随机激光的特点、发展历史和它的应用前景。文章以随机激光的理论为基础，描述了四种主要的用于随机激光研究的方法。     

Holographic particle image velocimetry (HPIV)

There are several well-known difficulties in forming and analysing holographic particle data in the micrometre and sub-micrometre size range. This paper suggests that these problems can be overcome by using a combination of research techniques. Firstly, it has been found that it is possible to record images of sub-micrometre particles using conventional photographic materials. Essentially, a diffraction limited optical component has been used to provide aberration free particle images. Secondly, the sensitivity of the holographic material has been increased with the use of specialized holographic processing chemicals. Thirdly, it has been found that it is possible to encode holoraphically double, slightly displaced, particle images using a pulse laser. Thus, Young's fringes can be obtained directly from the stored holographic data and the particle velocity can be measured directly from the hologram. Fourthly, the holographic particle data can be automatically analysed using a software programme. Finally, since the data is stored holographically, it is possible to obtain instantaneous three-dimensional particle velocity. This paper demonstrates that it is possible to perform holographic particle image velocimetry automatically, with only a small amount of pre-processing.     

Holographic storage of three-dimensional image and data using photopolymer and polymer dispersed liquid crystal films

We present holographic storage of three-dimensional(3D) images and data in a photopolymer film without any applied electric field.Its absorption and diffraction efficiency are measured,and reflective analog hologram of real object and image of digital information are recorded in the films.The photopolymer is compared with polymer dispersed liquid crystals as holographic materials.Besides holographic diffraction efficiency of the former is little lower than that of the latter,this work demonstrates that the photopolymer is more suitable for analog hologram and big data permanent storage because of its high definition and no need of high voltage electric field.Therefore,our study proposes a potential holographic storage material to apply in large size static 3D holographic displays,including analog hologram displays,digital hologram prints,and holographic disks.     

Edge-Preserving Denoising of Image Sequences

To monitor the Earth’s surface, the satellite of the NASA Landsat program provides us image sequences of any region on the Earth constantly over time. These image sequences give us a unique resource to study the Earth’s surface, changes of the Earth resource over time, and their implications in agriculture, geology, forestry, and more. Besides natural sciences, image sequences are also commonly used in functional magnetic resonance imaging (fMRI) of medical studies for understanding the functioning of brains and other organs. In practice, observed images almost always contain noise and other contaminations. For a reliable subsequent image analysis, it is important to remove such contaminations in advance. This paper focuses on image sequence denoising, which has not been well-discussed in the literature yet. To this end, an edge-preserving image denoising procedure is suggested. The suggested method is based on a jump-preserving local smoothing procedure, in which the bandwidths are chosen such that the possible spatio-temporal correlations in the observed image intensities are accommodated properly. Both theoretical arguments and numerical studies show that this method works well in the various cases considered.     

基于解码技术的全息显微术研究

提出了一种利用解码技术对全息显微畸变图像进行校正的方法。把全息记录中的显微镜预放大过程作为物光波产生畸变的编码过程;在波前再现过程中,用全息记录中的预放大显微镜对再现的赝实像再次放大进行解码,从而获得清晰的全息显微图像。实验验证了该方法的有效性。     

Theoretical Investigation on the Saturation Effects in Two-photon Pumping Random Lasers

A numerical analysis of the saturation effects of emitted light intensity in two-photon pumping random lasers is presented by adding the saturation item to modify the gain in the diffusive equation. Numerical results show that the emitted intensity reaches its saturation value in a short time interval with sufficient pumping. From the analysis of normalized emitted intensity and saturation intensity, one can obtain a method to control steady output intensity of two-photon pumping random lasing by adjusting some parameters of the random media     

超短脉冲激光光束在一维反射型体全息光栅中的衍射

基于Kogelnik的耦合波理论,研究了在色散效应的影响下,超短脉冲激光光束在反射型体全息光栅中衍射的性质.研究给出了衍射光及透射光在频谱域及时间域的振幅及强度分布、光栅的光谱宽度及衍射效率随光栅参量及入射条件的变化.数值研究的结果表明,在光栅记录介质色散效应的影响下,衍射光束的光谱宽度减小,脉冲展宽,衍射效率降低.通过适当的选取光栅参量及入射条件,可以控制衍射和透射光束的频谱和时间强度分布,得到满意的衍射和透射光束的带宽和波形,从而可以将其应用于脉冲整形等技术中.     

弱散射屏的像面散斑自相关函数特性的实验研究

在对随机弱散射屏进行表面参数的原子力显微镜测量和建立了门积分取样平均的随机光强自相关函数测量系统的基础上,对弱散射屏在严格像面和离焦像面上产生的散斑自相关函数进行了测量。发现在严格像面上,散斑平均颗粒的大小随表面粗糙度增加而减小,且光强自相关函数次极大的相关间隔宽度随粗糙度增加而减小;而次极大的超伏随粗糙度的增大而增大;在离焦像面上,离焦量的增加使光强的自相关函数下降变得平滑,并使极小值点和次极大点变得不明显或者消失。     

基于滤波成像的大视角数字全息技术

为提高数字全息再现像视角,提出一种基于滤波成像的数字全息技术来实现大视角的三维物体面型测量.利用离轴像面数字全息技术,通过在4F相干图像处理系统的空间频谱面处放置可移动的低通滤波器,使满足CCD分辨率的物光波与参考光波干涉形成全息图,并控制低通滤波及成像区域分别记录不同谱段的子全息图.再现时,首先对子全息图进行数字傅里叶变换,重构对应频谱段,并对频谱段进行拼接形成完整的物光频谱|而后通过数字再现获得大视角的数字全息再现像.利用该方法测量了圆柱形表面（光滑的缝纫针）的三维形貌,并取得了较好的实验结果.