光学扫描全息术的推广

给出了光学扫描全息术的基本原理。记录时用实时 FZP与物体强度透射率发生卷积从而产生扫描全息图 ;再现时用与记录时相对应的 FZP与全息图信号发生卷积即可再现出物体的信息。推广了光学扫描全息术 ,提出只要某一实时的光场强度分布函数具有如下性质 :(l)该函数中含有 x,y,z参量且相对于 z参量具有圆对称性 ;(2 )对于某一确定的 z参量 ,该函数的自相关是δ函数 ,就可以把该光场作为光学扫描全息术中的照明光场对物体进行扫描记录以得到扫描全息图。     

Twin-image elimination experiments for three-dimensional images in optical scanning holography

Twin-image elimination in the context of optical scanning holography has recently been proposed. The proposed technique involves simultaneously acquiring sine and cosine Fresnel holograms. A complex hologram is then formed by complex addition of the holograms, and twin-image rejection is predicted by computer simulations. An experimental verification of the technique by optical acquisition of the two holograms and subsequent reconstruction of the complex hologram digitally is reported. Three-dimensional image reconstruction without twin-image noise is demonstrated.     

CG光学扫描全息术和FZP光学扫描全息术分辨率比较

本文通过计算机仿真对ＦＺＰ 光学扫描全息术和ＣＧ 光学扫描全息术的横向和纵向分辨率进行了比较。无论是ＦＺＰ 还是ＣＧ 光学扫描全息术,其系统的分辨率与它们的环数有关,当环数越多时,分辨率越高。对于同样大小的ＦＺＰ 和ＣＧ,ＣＧ 光学扫描全息系统的分辨率比ＦＺＰ 光学扫描全息系统的分辨率要好     

基于光学全息指纹锁的设计与仿真

本文提出了一种基于光学全息的“指纹锁”,将其放置在智能卡的IC芯片前面,用于对用户的个人识别号(PIN码)进行预先加密和认证,和智能卡原有的数字加密算法相结合,可进一步提高信息存储和提取的安全性.该指纹锁是以指纹图像和随机相位板为密钥,记录在光折变晶体材料内的一组角度复用加密全息图.这种光学加密全息图与传统的角度复用全息图不同,其参考光兼有指纹密钥的振幅调制和随机相位调制,具有私密性好、携带方便、安全性高等优点.     

High resolution digital holography

In digital Fresnel holography, present specifications of charge-coupled device cameras require the incident beams to be quasi-parallel. That implies large speckle grain size and low lateral resolution in reconstructed images. Better lateral resolutions are demonstrated in our work, down to 8 μm, allowing the observation of sub-millimetre objects by digital holography. The experimental set-up built samples the incident light distribution with a definition of 500 pixels mm⁻¹. The maximum acceptable angle is then widened and the hologram recording and reconstruction distances are drastically reduced, as well as the speckle size. Interferometric holography was implemented for the measurement of the deformation of a sub-millimetre silicon cantilever and results in phase-contrasts imaging are also reported. The design of dedicated complementary metal-oxide-semiconductor active pixel sensor cameras is also discussed.     

Digital in-line holography for the characterization of flowing particles in astigmatic optical systems

An extended Generalized Fresnel Transform (GFT) is proposed to account for the astigmatism introduced by optical elements described, in the paraxial approximation, with a ray transfer matrix analysis. Generalized impulse response and generalized Fresnel transfer function propagators as well as sampling conditions are derived to properly implement this transformation. As a test case, the near-field diffraction patterns and in-line holograms produced by droplets flowing in a tube with cylindrical interfaces have been simulated. A best fitting approach is introduced to retrieve, from the propagated holograms, the 3D position and size of the droplets. Several hologram focusing indicators based on the analysis of droplets focus region are also proposed to further improve the estimation of the droplets position along the optical axis. Numerical simulations and experimental results confirm the applicability and accuracy of the proposed methods.     

Variable tomographic scanning with wavelength scanning digital interference holography

We present a new method for variable tomographic scanning based on the wavelength scanning digital interference holography (WSDIH). A series of holograms are generated with a range of scanned wavelengths. The object field is reconstructed in a number of selected tilted planes from each hologram, and the numerical superposition of all the tilted object fields results in a variable tomographic scanning. The scanning direction can be arbitrary angles in 3D space but not limited in a 2D plane, thus the proposed algorithm offers more flexibility for acquiring and observing randomly orientated features of a specimen in a WSDIH system. Experiments are performed to demonstrate the effectiveness of the method.     

复合扫描全息术及透过强散射介质三维成像研究

应用菲涅耳波带片光学扫描全息术原理,研究强散射介质中吸收体的三维成像.针对由成像物体强散射背景产生的背景噪音,提出复合扫描全息术成像方法.实验中应用这一方法,对嵌埋在浓度为1%,深度为1.7 cm的脂肪乳剂中的吸收体成像,得到了信噪比和对比度较好的再现像.在此基础上,对复合扫描全息成像系统的信噪比,对比度及分辨率等性能进行了深入的理论分析和实验测试.研究表明,与单一模式相比,复合扫描全息术在信噪比和对比度方面有较大改善,但分辨率还需进一步提高.     

光学扫描全息术研究进展

光学成像技术极大地拓展了人类的视觉极限,提高了人们观察和理解现实世界的能力。越多地获得目标的光学信息,对其的认识越充分。数字全息术是一种可以将样本的三维信息以二维全息图的形式编码记录下来的一种成像技术。通过获得由携带物体信息的物光波和参考光波叠加产生的干涉图案,可以以数字化的方式实现多种重建模态,例如图像恢复、相位成像和切片成像等。光学扫描全息术是一种独特的数字全息成像技术,通过主动式二维化扫描对三维物体进行成像,其完整的波前信息可以被单像素探测器记录,并基于光外差检测进行信号解调,从而恢复出复数全息图。对光学扫描全息术的最新进展进行介绍。首先,基于双光瞳成像系统,通过特殊的硬件和算法设计,提高光学成像系统的性能,如提高空间分辨率、缩短扫描时间。其次,基于计算成像原理,通过改进和优化全息像重建算法,实现高质量的图像恢复,主要涉及切片成像和三维成像等重建模态。第三,介绍光学扫描全息术的其他研究方向,并讨论该领域未来可能的发展方向。     

Compensation of body shake errors in terahertz beam scanning single frequency holography for standoff personnel screening

In the terahertz(THz) band, the inherent shake of the human body may strongly impair the image quality of a beam scanning single frequency holography system for personnel screening. To realize accurate shake compensation in imaging processing, it is quite necessary to develop a high-precision measure system. However, in many cases, different parts of a human body may shake to different extents, resulting in greatly increasing the difficulty in conducting a reasonable measurement of body shake errors for image reconstruction. In this paper, a body shake error compensation algorithm based on the raw data is proposed. To analyze the effect of the body shake on the raw data, a model of echoed signal is rebuilt with considering both the beam scanning mode and the body shake. According to the rebuilt signal model, we derive the body shake error estimated method to compensate for the phase error. Simulation on the reconstruction of point targets with shake errors and proof-of-principle experiments on the human body in the 0.2-THz band are both performed to confirm the effectiveness of the body shake compensation algorithm proposed.     

Impact of the spatial coherence on self-interference digital holography

Owing to the unique feature that the signal and reference waves of self-interference digital holography (SIDH) contain the same spatial information from the same point of object, compared with conventional digital holography, the SIDH has the special spatial coherence properties. We present a statistical optics approach to analyzing the formation of cross-correlation image in SIDH. Our study reveals that the spatial coherence of illumination light can greatly influence the imaging characteristics of SIDH, and the impact extent of the spatial coherence depends substantially on the recording distance of hologram. The theoretical conclusions are supported well by numerical simulation and optical experiments.     

准随机点阵二值化Gabor波带片聚焦特性的数值计算

 Fresnel波带片有多个焦点,作为单色器波长选择元件使用时会受到高级衍射的影响。而Gabor波带片只有一个焦点,有更好的聚焦特性,但制作难度较大,准随机点阵二值化Gabor波带片概念的提出则解决了这个问题。介绍了准随机点阵二值化Gabor波带片的设计,并利用优化的程序分别对Fresnel波带片和准随机点阵二值化Gabor波带片的聚焦特性进行了模拟计算,通过对计算结果进行分析比较,发现准随机点阵二值化Gabor波带片具有抑制高阶衍射的特性。     

惯性约束聚变实验中的层析成像技术研究

文章对惯性约束聚变(ICF)中的多方位成像的层析技术(CT)和编码成像技术在激光等离子体实验中的应用进行了研究．作者完成了以下工作：建立了多方位层析成像系统，自行编制三维图像重建的软件；采用三个方位的针孔相机对爆推爆靶内爆压缩过程进行成像，同时成功地获得了三个针孔图像，得到的直径压缩比约为3．且压缩的对称性很好；采用编码成像技术，在“神光Ⅱ”上成功地验证了菲涅耳波带片的可行性应用，并建立了激光热核聚变产生的α粒子和腔靶超热电子的菲涅耳波带片成像系统，获得了热核反应区的α粒子图像，并首次得到了厚壁腔靶的超热X射线图像．     

基于光时分复用技术的高速成像系统

提出了一种基于光时分复用技术的高速成像系统。飞秒激光器中心波长1557 nm,脉冲宽度90 fs,对USAF-1951分辨率板线性扫描成像,扫描频率为38.88 MHz。在连续时间序列编码放大显微成像技术的基础上,运用光时分复用技术,复制光脉冲信号并携带检测物体相同的空间信息。原光脉冲和复制光脉冲以相同的采样率分别采样,通过相应的数据处理将两次采样数据整合在一起还原图像。实验结果表明,与传统的超快成像方法相比,成像系统利用10 GHz的数字采样设备可以达到20 GHz的采样率,采样点数是传统超快成像方法的两倍。该方法有效克服了成像系统采样率不足的问题,提高了成像系统的空间分辨率。与此同时,该系统算法复杂程度不高,有利于进一步促进超高速成像技术的发展。     

大孔径声全息密集阵列的阵元数量去冗余方法

大孔径密集声全息阵列是实现对非平稳噪声成像的有效手段,通过现场快速成像可以掌握声场分布的动态特征。增加声阵列的孔径和阵元密度是提高近场声全息成像性能的主要措施,但随着声阵列阵元数量的增加,声压采集数据量增大,全息运算速度降低,全息成像动态性能下降,不利于现场即时成像分析。研究表明,在一定信噪比条件下,盲目增加阵元数量并不一定能提高近场声全息性能,为此,本文针对密集声全息阵列的阵元数量冗余问题进行研究,提出最优阵元数量估算方法,并采取去冗余处理。本文仿真和实验验证表明:针对一定信噪比条件下的密集阵列去冗余方法实际有效,可以在不降低近场声全息成像性能的前提下,降低运算量,提高全息成像速度,对于非平稳噪声的现场声全息成像测试具有实用意义。     

Defining the size and location of the slit in rainbow holography

A simple method is described for defining the size and location of the slit in a rainbow holography optical system in order to guarantee the optimal observation conditions of the reconstructed image. A brief explanation of the basic principles of rainbow holography is given and the projection of viewing slits and pseudoscopic, or orthoscopic, images is considered. An application of the method for afocal systems used in rainbow holography is presented.     

共口径双通道红外扫描成像光学系统

对双波段红外扫描成像光学系统进行了研究,结合三次成像技术和100%冷光栏效率技术,设计了一个共口径双通道红外扫描成像光学系统。该系统包括前端共用的双反射系统、分束镜、准直镜组、扫描镜和成像镜组。光波经过双反射系统在主镜之后被分束镜分成中波红外通道（3 m～5 m）和长波红外通道（10 m～12 m）,经准直镜组及成像镜组会聚探测器上,实现中波红外系统与长波红外系统共口径同步成像。设计结果表明,长波红外系统传递函数在18 lp/mm处达到0.4以上,中波红外系统传递函数在18 lp/mm处达到0.78以上,满足实际应用的要求。     

二元计算全息法产生复杂无衍射光束

无衍射光束是一种能在自由空间稳定传输的光束。近来,一类具有复杂光学形态的无衍射光束被引入,比如马蒂厄光束、抛物光束、非对称贝塞尔光束等。为了产生具有复杂结构的无衍射光束,需要对光波进行复振幅调制,即同时调制光波的振幅和相位。但目前的商用光学调制元件只能调制光波的振幅或相位。本文基于二元计算全息法,编码二维复透过率函数分布,构建了具有复振幅调制功能的二元实振幅非负计算全息图。利用实验室自主研发的投影成像光刻系统,对银盐干板进行曝光处理,经显影、定影处理,将其加工为相应的振幅掩模板,用来产生精确的具有复杂结构的无衍射光束。以无衍射马蒂厄光束为例,采用罗曼型迂回相位编码方法,在全息图每个抽样单元内开一个矩形通光孔径,通过改变通光孔径的面积来对复值光波的振幅进行编码,通过改变通光孔径中心偏离抽样单元中心的距离,来对复值光波的相位进行编码。最终构建了两种产生马蒂厄光束的典型二元实振幅计算全息图,其像素数高达28 000 pixel×28 000 pixel。之后利用加工好的振幅掩模板,准确、方便、高效地产生了的椭圆系数q=10,拓扑荷数m=0与m=1的第一种偶型马蒂厄光束,其他类型的马蒂厄光束可...     

Optical receiving solution for optical scanning lag effect of LADAR

Optical scanning plays a very important role in LADAR system for large field of view (FOV). But it introduces the optical scanning lag effect due to the optical scanning and the time delay between laser pulse transmitting and receiving. Optical scanning lag angle will make a part of received optical energy fall out of the optical sensitive area of detector, which will greatly degrade the detecting performance of LADAR in many cases. Optical scanning lag effect and optical scanning lag angle are firstly computational analyzed in detail in this paper. A novel optical receiving design approach is proposed, and the experimental result is given.     

太赫兹数字全息术的研究进展

随着太赫兹成像技术的不断成熟,其空间分辨率和系统信噪比逐渐提高,成像速度逐渐加快,光学信息获取能力逐渐变强,人们对太赫兹成像在基础研究和工业应用的开发也逐渐深入。本文综述了近年来科研人员利用太赫兹数字全息成像系统进行的部分研究工作,包括对平板太赫兹元件的性能表征、对光控太赫兹元件的功能验证、对衍射太赫兹场中的纵向分量进行观测、以及对金属亚波长器件的太赫兹表面波进行分析。这些工作的完成对于太赫兹集成系统的研究和太赫兹成像技术的应用都具有积极的推动作用。