全息照相再现实象分析

全息照相再现实象分析胡德敬（同济大学物理系上海２０００９２）本文根据全息照相的成像理论对再现实像的形成条件、最佳记录光路、观察方法和特点作一分析，其结果和实验一致．一、理论根据图１中全息干板位于ｘｏｙ平面，物点和参考光波源分别用Ｏ（ｘ０，ｙ０，ｘ０）...     

白光再现全息照相

简述了激光全息照相的原理,设计出全息照相的拍摄光路,探索出能成功拍出全息图的方法以及能实现白光再现的实验参数。总结出拍摄反射全息的条件,并能了解全息照相与普通照相的区别,以及全息照相的应用及开拓。     

拍摄白光再现全息图的一种实验方法

白光再现全息图的干涉极大值在感光介质中的分布几乎平行于乳胶表面,间距约为半个波长(在氦氖激光器波长为632.8nm的条件下,间距d约为0.3μm)。因此要求记录介质有较高的分辨率,而且要求形成反射全息图的全息实验台和有关的光学元件有极高的机械稳定性。教学用简易全息实验台常达不到要求,因此很难拍摄成功白光再现全息图。为了提高学生对于全息实验的兴趣,我们找到了一种在简易全息实验台上拍摄成功白光再现全息图的方法。现介绍如下。用一个书写投影仪上的反光装置,将其     

全息照相再现虚像光信息与原物光信息比较

设计出一种可将全息照相再现虚像与其原物并排同步拍摄的光路 ,通过实验验证全息照相的再现虚像的光信息和原物的光信息一致。     

全息照相实验问题探讨

全息照相理论比较复杂，特别是在对实验现象的解释上，一些教材写得不够清楚.本文利用近代全息理论，对实验现象进行深入细致的分析与讨论.一、全息理论1.几何描述如图1（a）所示布置记录光路.为使讨论的问题简化并有利于再现实像，令参考光垂直人射干版.从图1（b）可看出，相邻干涉条纹的间距（光栅常数）为式中θ0为两束相干光的夹角，λ为光波波长.再现时，让与参考光相同的再现光也垂直入射在图1全息片上.其衍射角θp由光栅方程决定如图2所示，当k=0时，θp=0，表明零级衍射沿着再现光方向；当k= 1时，θ＋1=θ0，表明 1级衍射沿着原物…     

预成像数字全息测量大物体三维形貌

为了扩大数字全息三维形貌测量的视场,提出了一种预成像的方法.物体先被成像镜头成一缩小的实像,再使用离轴菲涅耳数字全息对此实像进行全息记录.采用倾斜照明光的方法使两次数字全息的再现像之间产生相位差,通过相位去噪和去包裹处理从相位差中提取物体的三维形貌数据.实验证明,预成像方法使测量视场的大小得到了至少一个数量级的提高,采用离轴菲涅耳数字全息降低了测量系统对环境稳定性的要求.     

全息照相实验的探讨

本文简要介绍了全息照相的基本原理,分析了影响激光全息照相实验的诸因素,并对这些因素进行了深入的探讨。实验中采用有良好散射性能的硬币为被拍摄对象,以RSP-I型红敏光致聚合物全息干板为记录介质,使得学生实验成功率大大提高,取得非常好的实验教学效果。     

非线性介质对粒子场同轴全息成像的影响

 通过理论分析和实验验证,研究了非线性折射率介质对粒子场同轴全息成像的影响。利用粒子场同轴夫琅和费全息记录和光束在非线性介质中传输的波动方程,得出了光波的复振幅和强度分布。数值模拟了介质在线性和非线性时全息记录的情况,并进行了实验验证。结果表明：光波经非线性介质传输后,全息干板记录到粒子场的再现图像,这为高功率激光应用于全息照相提供参考,原因是高功率脉冲激光聚焦易击穿介质产生非线性传输。     

体积全息图中的光子禁带

利用光子晶体的概念和方法分析光学全息,用光子晶体的带结构解释了体积全息图的性质.与超晶格不同,全息光子晶体的介电常量是渐变而不是突变的.着重讨论了一维非倾斜反射全息图在再现光不同角度入射情况下禁带结构的性质,通过基元反射全息实验的验证,证明体全息的禁带分析与实验结果符合得很好. 关键词： 体积全息图 光子晶体 禁带     

白光再现激光全息照相的实验研究

以光的干涉和衍射为基础,讨论白光再现激光全息照相的原理,设计拍摄不同物体白光再现全息图的光路,探索能成功拍出白光再现反射全息图的条件和方法,并通过实验证明其可行性。     

动态微粒场诊断用全息光路的设计与分析

本文分析了动态微粒场测试的特点,设计了一种适合于动态微粒场用脉冲激光全息诊断的全息光路,并从理论上进行了分析。使用这种全息光路记录的微粒场全息图,当用记录参考光,而不是它的共轭光照明再现时,就能获得微粒的实象,因而,使得参考光类型的选择更加灵活。同时,由于光路设计上还考虑了参物光之间的空间相干性的匹配,故降低了对激光器横模的要求。     

Acoustic field imaging by light reflection at the free surface of a liquid

In this paper we present a novel technique for acoustic field imaging. This technique is based on reflection of a collimated laser beam at the free surface of a liquid. The reflected beam becomes phase modulated by the acoustic wave as in acoustical holographic systems. We do not use a reference acoustical beam for holographic reconstruction but we observe this phase modulation using dark-field techniques. It gives a measurement of the acoustic field power as a function of the position. The authors have built an optical imaging system and carried out experiments with piezocomposite transducers. The technique presented in this work is able to give fast quantitative information about the performance of individual ceramic rods of the piezocomposite.     

Experimental investigation of the closest parallel pulses in holographic femtosecond laser processing

In holographic femtosecond laser processing, diffractive parallel pulses are distorted by phase discontinuities and mutual interference between the neighborhoods in the reconstructed image of a Fourier computer-generated hologram when the interval is smaller than the beam diameter. We investigated holographic fabrication on a glass surface using parallel pulses with different intervals. We found the closest parallel pulses with sufficient separation to avoid mutual interference in holographic femtosecond laser processing. The minimum interval was 2.8 times larger than the diffracted beam diameter. The experimental results were also supported by a computer simulation. Our findings will be very useful in the design of holographic laser processing systems.     

Collimation Characteristics of Planar Microlens for Parallel Optical Interconnect

We evaluated the collimated beam quality of a planar microlens (PML) for parallel optical interconnect systems. It has been confirmed that the divergence beam from a single mode fiber was collimated by single PML and propagated with good beam quality by about 10 mm, which is the nominal length of microoptics components considered. The divergence beam from a vertical cavity surface emitting laser was collimated using stacked PML and the collimated beam width of 100 μm was obtained. The collimated beam profile was good enough for low loss beam interconnect in a micro-optical bench scheme.     

Comparison of the laser ablation process on Zn and Ti using pulsed digital holographic interferometry

Pulsed digital holographic interferometry has been used to compare the laser ablation process of a Q-switched Nd-YAG laser pulse (wavelength 1064 nm, pulse duration 12 ns) on two different metals (Zn and Ti) under atmospheric air pressure. Digital holograms were recorded for different time delays using collimated laser light (532 nm) passed through the volume along the target. Numerical data of the integrated refractive index field were calculated and presented as phase maps. Intensity maps were calculated from the recorded digital holograms and are used to calculate the attenuation of the probing laser beam by the ablated plume. The different structures of the plume, namely streaks normal to the surface for Zn in contrast to absorbing regions for Ti, indicates that different mechanisms of laser ablation could happen for different metals for the same laser settings and surrounding gas. At a laser fluence of 5 J/cm², phase explosion appears to be the ablation mechanism in case of Zn, while for Ti normal vaporization seems to be the dominant mechanism.     

准直高功率激光束斜程大气传输中的非线性热畸变效应

本文根据波动光学理论,利用实际大气参数对准直高功率激光在斜程上行大气传输中的非线性热畸变效应进行了数值分析,结果表明,在上行大气传输中,尽管大气气体吸收系数较小,从而产生的热畸变效应也较弱,但它将导致激光光束位相畸变和发散角的显著增大,因此对远距离传输的光束将产生非常严重的不利影响。     

半导体激光器光波准直特性研究

分析了半导体激光器光波经准直透镜的传输特性,对影响准直光束质量的主要因素作了深入讨论,并在实验上利用小口径大数值孔径透镜获得了高准确直度的光束。     

Laboratory simulation of atmospheric turbulence-induced optical wavefront distortion

Real-time liquid crystal television-based technique for simulating optical wavefront distortion due to atmospheric turbulence is presented and demonstrated. A liquid crystal television (LCTV) operating in the “phase mostly” mode was used as an array of spatially correlated phase delays. A movie of the arrays in motion was then generated and displayed on the LCTV. The turbulence simulation system was verified by passing a collimated and doubled diode pumped Nd:YVO₄ laser beam (532 nm) through the transparent LCTV screen. The beam was then passed through a lens and the power spectra of the turbulence information carrying beam was detected as a measure of the far-field distribution. The same collimated laser beam, without the LCTV, was also transmitted down an open-air range and the power spectra detected as a measure of a real far-field distribution. Accepted turbulence parameters were measured for both arrangements and then compared.     

Formation of Hot Images in Laser Beams through a Self-defocusing Kerr Medium Slab

A nonlinear hot image is usually thought as of a special case of self-focusing, and thus occurs when a laser beam propagates through a slab of self-focusing medium. Here we show theoretically that a hot image may also be formed by a thin slab of self-defocusing medium. The physical origin for this hot image formation is akin to the in-line volume-phase holographic imaging due to the intensity-dependent refractive-index modulation of the self- defocusing medium. NumericM simulations confirm the theoretical prediction and further identify the dependence of the hot image on the beam power, the modulation depth of obscuration and the thickness of self-defocusing medium. The analysis presented here brings new insight into the physics of hot image formation in the high power laser system.     

Study of the parameters of a difference image in the presence of a linear phase shift

The spatial filtering in the localization range of the holographic lateral shearing interferograms of a solid object shows that the effect of the subtraction of the compared original data arrays is realized in the presence of a filtering aperture in the center of a dark fringe [1, 2]. Methods for the holographic subtraction of the images involving the detection and spatial filtering in the Fourier plane of the optical system are proposed and realized in [3–5]. Thus, the difference data can be reconstructed with a narrow (unexpanded) laser beam. However, a relatively high level of speckle noise in the difference image is caused by the spatial filtering with a small aperture (laser beam) in the minimum of the superposition field in the Fourier hologram plane. The detection of double-exposed Fourier holograms with a linear phase shift and the effect of the size of the filtering reconstructing beam on the resolution of the difference image are studied. In addition, the application of the multiple exposure for the broadening of the interference maxima is analyzed.