Stokes参量数字全息法实现相位物体成像

为实现对相位物体的无损检测和成像,克服数字同轴全息相位物体成像技术在消除零级像和孪生像的干扰时存在的系列问题,提出一种基于Stokes参量的新的数字同轴全息技术。该方法区别于传统的利用干涉光场来记录原始像项的数字全息方法,通过测量物参光合成光束的Stokes参量来分别得到这两束光的振幅和相位差,从而准确、唯一地获得原始像项;再利用数字再现即可重构物光的振幅和相位信息。实验中对弱吸收的相位样品进行了测量,得到样品清晰的振幅和相位分布。结果表明,采用该方法对相位物体进行数字全息再现,可以克服传统同轴全息图中零级像和共轭像对相位物体信息的严重干扰,对于提取相位物体的振幅和相位信息是可行和有效的。     

基于数字全息及复用技术的全场偏振态测试方法

提出了一种在数字全息记录系统中利用偏振和角分复用技术对光场进行偏振态检测的方法. 将全息系统中的一束参考光分为偏振方向相互正交、初相位相同的两束光, 并分别与物光相同偏振方向的两个分量干涉, 形成两幅子全息图, 同时记录在一帧画面中. 为了分开记录到的物光两个分量, 系统中利用了角分复用技术, 即在两束参考光中引入不同载频, 使物光两分量的频谱位于全息图频谱面的不同区域. 通过滤波、逆傅里叶变换和衍射计算, 获取距离全息图不同位置处物光两正交分量复振幅信息. 利用复振幅信息, 可以构建被测物光的斯托克斯参量和琼斯矢量, 从而表征物光的偏振态. 实验中, 通过对一束椭圆偏振光进行偏振态测量以及对该光束在不同空间位置处的偏振态进行表征, 表明该方法可以实现光束偏振态全场测试, 并且具有较高的可靠性. 关键词： 数字全息 偏振态 琼斯矢量 斯托克斯参量     

物光的偏振性对全息记录质量的影响

通过对菲涅耳三维漫反射全息记录光路中物光与参考光偏振状态的实验检测，发现线偏振的激光被不同表面材料的物体散射和漫反射后变成“部分偏振光”，几乎所有目标物都有显著的消偏振现象，全息干板上实际记录的是线偏振的参考光与“部分偏振”的物光形成的相干度较低的干涉条纹。物光偏振度的大幅度下降影响干涉条纹的衬比度，并增加全息图的噪声。给出实验方案和检测光路，采用在参考光路中插入1/4波片的方法，可充分利用非偏振物光各个振动方向的光能，提高条纹的衬比度。     

基于模糊聚类和证据理论的光谱偏振图像分类

为了将光谱偏振信息用于物质分类,提出了一种无监督聚类融合算法.算法结合偏振信息的特性,首先对Stokes参量中的非偏振光强参量、线偏振度参量、偏振角参量进行无监督模糊c均值聚类(Fuzzy C-mean,FCM),利用目标表面的偏振特性以及聚类结果分配置信指派,然后对这些置信指派进行加权融合.仿真实验表明了算法的有效性.     

吲哚俘精酰胺的偏振全息图像光存储实验研究

在吲哚俘精酰胺/PMMA薄膜上记录了同偏振全息和正交偏振全息图，获得了它们的再现衍射像.实验结果表明：吲哚俘精酰胺具有光致各向异性，可以进行正交偏振全息记录.在偏振全息中，衍射光的偏振方向依赖于物光和再现光的偏振方向，衍射像的噪声主要来源于再现光照射到样品上引起的散射.正交偏振全息可以得到比同偏振全息更高信噪比的衍射像.存储于样品上的全息图在室温下黑暗处至少可以保存五个月而衍射效率无明显下降.结果表明，吲哚俘精酰胺是一种可用于偏振全息的可擦重写记录介质. 关键词： 偏振全息 光致各向异性 俘精酸酐 光致变色     

基于双色光照明的单曝光同轴数字全息技术

提出了一种基于双色光照明的单曝光同轴数字全息技术。在红绿蓝三色中,任选两种波长的光来照射物体,采用彩色CCD记录双色同轴全息图,然后经过三基色分离数字处理,可得到两幅不同波长的同轴全息图。用角谱衍射理论对该技术进行了分析,表明在降低物参光振幅比的条件下,通过对同轴数字全息图求自然对数,可近似得到衍射物光及其共轭之和,其误差与物参光振幅比有关。取两幅不同波长的同轴数字全息图,经自然对数处理后,用传递函数可以很好地重构出物体图像,给出了具体的数字处理算法。用仿真实验,模拟了该技术的全息记录和处理过程,得到重构图像的峰值信噪比(PSNR)为14.2 dB。结果表明该方法可以去除孪生衍射像干扰,可以实现清晰的单曝光同轴全息成像。最后,分析了再现像中噪声产生的原因。该技术可用于基于同轴全息的实时成像与动态测量。     

弹光调制器准单色光波偏振测量与仿真

弹光调制器(Photoelastic Modulator,PEM)互差频调制的新型偏振测量方法,能够同时实现三个斯托克斯光谱偏振参数测量,克服了现有方法的无法用阵列探测器有效采集,调制频率高的缺点,保留了原有弹光调制器偏振测量的优点。文章以光学系统的准单色光的偏振特性以及常用的偏振分析方法为基础,引入了Stokes矢量来表示入射光波的偏振特性。分析了弹光调制器实现偏振测量新方法的原理,利用三个弹光调制器工作在互相差异的频率上,对偏振光进行差频调制,产生载有偏振信息的低频分量,再通过锁相放大即可得到偏振信息,并给出利用MATLAB模拟仿真实现Stokes参量复原的过程。理论分析及仿真结果证明了该方法在理论上的可行性。     

高光谱偏振成像全Stokes参量获取新方法（英文）

考虑到现有Stokes参量获取方法测量速度慢、测量精度低、系统结构复杂等特点,提出了一种基于双液晶可调相位延迟器(liquid crystal variable retarder,LCVR)和声光可调滤波器(acousto-optic tunable filter,AOTF)的光谱偏振成像系统中全Stokes参量的新获取方法。从AOTF和LCVR的工作原理出发,介绍了系统的基本探测原理;根据偏振分析提出了快速获取全Stokes参量的新方法——该方法选取四个固定的LCVR控制电压,同时控制两个相同的LCVR对光波进行相位调制,得到四组(八个)两两相同的相位延迟量即可求得Stokes参量。此外,设计了能够稳定输出均方根为0~+8.72V连续可调方波的LCVR控制器,并对其进行定标,实现了不同波长下光波的精确调制。搭建实验样机,以偏振方向分别为0°,90°和45°的三个偏振片P_1,P_2,P_3作为偏振测量目标,测得了波长为632nm时的全Stokes参量图;以画有夹角为30°的红色、绿色、蓝色三色线条的实验板作为光谱测量目标,对400~750nm光谱范围的71个通道(光谱带宽为5nm)进行光谱成像,得到了与红色、绿色和蓝色的分析谱段范围相一致的光谱曲线。结果表明,该系统不仅可以快速准确地获取全部Stokes参量,而且系统结构简单、成像质量良好。     

偏振敏感材料中具有圆各向异性的偏振全息光栅

在向列相液晶中掺杂质量分数约0.2%的偶氮侧链型聚合物制成偏振敏感材料,使用正交圆偏振光记录了具有圆各向异性的一维偏振全息光栅,用线偏振光探测偏振全息光栅,得到正,负一级衍射光也为线偏振光,且偏振态与探测光和零级偏振态相互正交,可以运用琼斯矩阵理论加以解释.偏振全息光栅可由外加电场控制衍射级的变化,即在外加电场作用下,正、负一级衍射产生了90°的相位差.在频率6.05 Hz、电压2.2 V的外场作用下,衍射级的极值振荡变化.     

高光谱偏振成像全Stokes参量获取新方法

考虑到现有Stokes参量获取方法测量速度慢、测量精度低、系统结构复杂等特点,提出了一种基于双液晶可调相位延迟器(liquid crystal variable retarder,LCVR)和声光可调滤波器(acousto-optic tunable filter,AOTF)的光谱偏振成像系统中全Stokes参量的新获取方法。从AOTF和LCVR的工作原理出发,介绍了系统的基本探测原理;根据偏振分析提出了快速获取全Stokes参量的新方法--该方法选取四个固定的LCVR控制电压,同时控制两个相同的LCVR对光波进行相位调制,得到四组(八个)两两相同的相位延迟量即可求得Stokes参量。此外,设计了能够稳定输出均方根为0~+8.72 V连续可调方波的LCVR控制器,并对其进行定标,实现了不同波长下光波的精确调制。搭建实验样机,以偏振方向分别为0°,90°和45°的三个偏振片P₁,P₂,P₃作为偏振测量目标,测得了波长为632 nm时的全Stokes参量图;以画有夹角为30°的红色、绿色、蓝色三色线条的实验板作为光谱测量目标,对400～750 nm光谱范围的71个通道(光谱带宽为5 nm)进行光谱成像,得到了与红色、绿色和蓝色的分析谱段范围相一致的光谱曲线。结果表明,该系统不仅可以快速准确地获取全部Stokes参量,而且系统结构简单、成像质量良好。     

Dynamic recording of a digital hologram with single exposure by a wave-splitting phase-shifting method

The wave-splitting phase-shifting digital holography using a pixelated microretarder array is proposed. By using four intensity images recorded by the pixelated microretarder array, Stokes parameters of the incident wave can be calculated. The fully complex amplitude distribution of the object wave can be obtained by using Stokes parameters, if the polarization states of the object and reference waves are linear and orthogonal. Two sets of experimental results are provided to verify the feasibility of the proposed method. One is the result for a movie recording using a CW laser and the other is the result for instant recording using a single pulsed laser.     

散射光彩色数字全息光学系统及波面重建算法研究

令物体表面为散射面,参考光及重建光为球面波,详细研究了离轴数字全息物光场重建平面的光波场.导出物光、共轭物光及零级衍射光分布与光学系统参数的关系.根据彩色数字全息的特点,提出抑制零级衍射干扰的光学系统设计方法,并且对一种能够避免插值误差的波面重建算法进行了优化研究,给出了相应的实验证明.     

Analysis of Polarization State by Digital Holography with Polarization Modulation

The digital holographic technique is applied to analyze the spatial distribution of polarization state of light transmitted through anisotropic objects using an orthogonal linearly polarized reference beam. The polarization orientation of reference beam is switched by an optical fiber Faraday rotator for successive hologram recording. To confirm the principle of polarization analysis, a quarter wave plate (QWP) is used and the distribution of polarization state over the object surface is analyzed for various orientations of the QWP. By providing an area of a known polarization for a part of the object wave as a reference, a phase drift of the reference waves can be evaluated and compensated for using the reference area. The principal axis and ellipticity of polarization ellipse are calculated and compared with their theoretical values. A good agreement between the experimental and theoretical values is observed.     

Dynamic characterization of MEMS diaphragm using time averaged in-line digital holography

In this paper dynamic characterization of a MEMS diaphragm is investigated using lens-less time averaged in-line digital holography. The analysis and capability of the numerically reconstructed amplitude and phase information from in-line time averaged holograms as applied to MEMS vibration are presented. Particularly the effect of mean static state on the phase in time averaged digital holography is explored. A novel double exposure method is also demonstrated using a diverging object wave suitable for dynamic characterization of small size objects. A phase jump in the static deformation fringes in the vibrating regions is observed and described and can be used for precise analysis of vibration mode shape under simultaneous presence of mean static deformation. A simple and robust tool for dynamic optical metrology of MEMS devices and micro-objects using time averaged in-line digital holography is thus proposed.     

Dual-channel in-line digital holographic double random phase encryption

We present a robust encryption method for the encoding of 2D/3D objects using digital holography and virtual optics. Using our recently developed dual-plane in-line digital holography technique, two in-line digital holograms are recorded at two different planes and are encrypted using two different double random phase encryption configurations, independently. The process of using two mutually exclusive encryption channels makes the system more robust against attacks since both the channels should be decrypted accurately in order to get a recognizable reconstruction. Results show that the reconstructed object is unrecognizable even when the portion of the correct phase keys used during decryption is close to 75%. The system is verified against blind decryptions by evaluating the SNR and MSE. Validation of the proposed method and sensitivities of the associated parameters are quantitatively analyzed and illustrated.     

数字像面全息与同轴全息实验研究

通过采用数字像面全息与同轴全息技术拍摄透明物体以及不透明物体的全息图,并在计算机上再现。结果表明,当记录较小物体的全息图像时像面全息技术更加合适。     

Parallel-quadrature phase-shifting digital holographic microscopy using polarization beam splitter

We present a digital holography microscopy technique based on a parallel-quadrature phase-shifting method. Two π/2 phase-shifted holograms are recorded simultaneously using polarization phase-shifting principle, slightly off-axis recording geometry, and two identical CCD sensors. The parallel phase-shifting is realized by combining circularly polarized object beam with a 45° degree polarized reference beam through a polarizing beam splitter. DC term is eliminated by subtracting the two holograms from each other and the object information is reconstructed after selecting the frequency spectrum of the real image. Both amplitude and phase object reconstruction results are presented. Simultaneous recording eliminates phase errors caused by mechanical vibrations and air turbulences. The slightly off-axis recording geometry with phase-shifting allows a much larger dimension of the spatial filter for reconstruction of the object information. This leads to better reconstruction capability than traditional off-axis holography.     

Reconstruction of in-line digital holograms from two intensity measurements

We propose a new method based on in-line digital holography for the reconstruction of a wave front from only two intensity recordings. The simulation result shows that this method works well when the object wave is weak compared with the reference wave. This technique can be employed for real-time imaging.