数字全息技术的原理和应用

数字全息是随着现代计算机和CCD技术发展而产生的一种新的全息成像技术．文章主要介绍数字全息技术的基本原理，数字全息重建中的主要方法以及数字全息技术以其独特的优点在各个领域中的应用．     

Methodology for analysis of displacement using digital holography

Digital holography is applied to make microdisplacement determination of a steel bar and an aluminum sheet. The displacement of aluminum sheet is made under immersion conditions in water and air. An experimental installation is presented for digital hologram registration with plane reference beam, using a CCD camera as detector. The “HOLODIG” computing system was developed for digital reconstruction of the image using the direct method, the intensity and phase image and interferograms were obtained. Taking into account the phase interferogram and making the unwrapping, the phase was determined for every point of the study surface. As examples of method application, the displacement of a square section steel bar, tested in air, and an aluminum sheet, tested in air and submerged in water, was determined. Experimental values of the displacement obtained agree with the applied ones. In the case of aluminum plate submerged in water, the magnitude of the measured displacement is proportional to water refraction index.     

Measurement of static and vibrating microsystems using microscopicTV holography

This paper describes a microscopic TV holographic arrangement to study the static and vibrating microsystems. In the optical setup, the object beam and the reference beam arms are provided with a phase shifting mirror and a bias phase modulation mirror to carry out the measurement of the out-of-plane deformation and the vibration amplitude fields, respectively. A long working distance microscope is used in the setup for magnifying and imaging the objects on to the CCD camera. For static fringe analysis, the system is used in double exposure subtraction mode of operation, while for vibration fringe analysis, it is used in the time average contrast reversal refreshing mode of operation. An improved approach for qualitative analysis of time averaged fringes helps in reducing the number of frames required for analysis. The usefulness of the system is demonstrated by examples of static and vibration measurements for different microobjects.     

Quantitative evaluation of two-dimensional dynamic deformations using digital holography

An optical system for the parallel evaluation of in- and out-of-plane dynamical deformations will be described. A double pulse laser with pulse separation in the microsecond range is used for the investigations. Two separate interferograms of an object under test, in its undeformed and deformed state, are recorded in a few microseconds. The object is illuminated from two different directions and imaged onto a CCD sensor. This produces two sensitivity vectors. The reference beams have different directions in order to produce two directional spatial carriers. The Fourier method is used for quantitative evaluation, and the measurements along different sensitivity vectors are separated in the Fourier domain. The phases of the two interferograms are obtained from the complex amplitudes and the two dimensional deformation is calculated from the phases. Experimental results are presented.     

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.     

数字全息术测定涡旋光束拓扑电荷数

提出了一种基于数字全息技术测定涡旋光束拓扑电荷数的方法.该方法通过数字全息技术获取涡旋光束和参考光的全息图并重构出涡旋光束的波前相位,判定相位围绕相位奇点的周期性分布来测定涡旋光束的拓扑电荷数.在拓扑电荷数取值分别为整数和分数的情况下,通过对数值模拟和实验结果的比较,表明该方法能够较准确地测定出拓扑电荷数.     

Proposal for underwater structural analysis using the techniques of ESPI and digital holography

The purpose of this article is to study the application of the holographic interferometry techniques in the structural analysis of submarine environment. These techniques are widely used today, with applications in many areas. Nevertheless, its application in submarine environments presents some challenges. The application of two techniques, electronic speckle pattern interferometry (ESPI) and digital holography, comparison of advantages and disadvantages of each of them is presented. A brief study is done on the influence of water properties and the optical effects due to suspended particles as well as possible solutions to minimize these problems.     

Hardness of materials at high temperature and high pressure

The intrinsic character of the correlation between hardness and thermodynamic properties of solids has been established. The proposed thermodynamic model of hardness allows one to easily estimate hardness and bulk moduli of known or even hypothetical solids from the data on Gibbs energy of atomization of the elements or on the enthalpy at the melting point. The correctness of this approach is illustrated by an example of the recently synthesized superhard diamond-like BC₅ and orthorhombic modification of boron, γ-B₂₈. The pressure and/or temperature dependences of hardness were calculated for a number of hard and superhard phases, i.e. diamond, cBN, B₆O, B₄C, SiC, Al₂O₃, β-B₂O₃ and β-rh boron. Excellent agreement between experimental and calculated values is observed for temperature dependences of Vickers and Knoop hardness. In addition, the model predicts that some materials can become harder than diamond at pressures in the megabar range.     

高平均功率电光开关晶体热畸变分析

深入分析了方板构型的电光开关晶体在高功率载荷条件下的热畸变行为,讨论了光强分布对热效应的影响。以KDP晶体为例,分别计算了激光束光强为高斯分布和均匀分布时晶体的温升、相应的热应力分布、波前畸变以及热退偏。结果表明,光强的分布形式对波前畸变和热退偏的影响是不同的。相对于光强均匀分布的激光束,高斯光束减缓了光斑边沿处的温度梯度,产生的热应力较小,因此可以减弱热退偏效应;另一方面,在光束口径范围内,高斯光束产生了附加的温度分布非均匀性,因而波前畸变会大一些。     

Phase transition of ZnS at high pressures and temperatures

The high-pressure behaviour of zinc sulphide, ZnS, has been investigated, using an in situ X-ray powder diffraction technique in a diamond anvil cell, at pressures and temperatures up to 35 GPa and 1000 K, respectively. The pressure-induced phase transition from a zincblende (B3) to a rocksalt (B1) structure was observed. This transition occurred at 13.4 GPa and at room temperature, and a negative dependence on temperature for this transition was confirmed. The transition boundary was determined to be P (GPa) = 14.4 ? 0.0033 × T (K).     

Real-time non-destructive testing of phase objects using four-wave mixing with photorefractive BGO crystals

Real-time non-destructive testing of phase and transparent objects using degenerate four-wave mixing with photorefractive BGO crystals is described. Some quantitative results of thickness variations of phase objects such as a thin optical wedge and a thin BGO crystal are also given.     

Structure changes in vacancy-rich titanium monoxide at high pressures and high temperatures

Abstract

Powdered samples of TiO_0.82, TiO_1.04 and TiO_1.25 having the cubic rocksalt-type structure with high concentration of vacancies randomly distributed were held at combined conditions of high pressure, ranging from 1 GPa to 8 GPa, and high temperature, ranging from 973 K to 1173 K, and structural changes occurring were investigated by synchrotron radiation diffraction at the conditions and by conventional X-ray diffraction after the samples were brought back to ambient condition. Pressure has been shown to suppress formation of ordered arrangements of vacancies in all the samples and lead to precipitation of a hexagonal δ-Ti₃O₂ in TiO_0.82 and TiO_1.04 and precipitation of a corundum-type Ti₂O₃ in TiO_1.25. Irreversible change in the lattice parameter of the remaining rocksalt-type structure has been observed which is due to partial annihilation of vacancies under pressure.     

Measurement of the bulk acoustic properties of fibrous materials at high temperatures

It is common for fibrous porous materials to be used in high temperature applications such as automotive and gas turbine exhaust silencers. Understanding the effect of temperature on the acoustic properties of these materials is crucial when attempting to predict silencer performance. This requires knowledge of the bulk acoustic properties of the porous materials and so this article aims to quantify the effect of temperature on the bulk acoustic properties of three fibrous materials: rock wool, basalt wool and an E-glass fibre. Measurements are undertaken here using a standard impedance tube that has been modified to accommodate temperatures of up to 500 °C. It is shown that measured data for the bulk acoustic properties may be collapsed using a standard Delany and Bazley curve fitting methodology provided one modifies the properties of the material flow resistivity and air to account for a change in temperature. Moreover, by using a previously proposed power law describing the dependence of the flow resistivity with temperature, one may successfully collapse data measured at every temperature and obtain the Delany and Bazley coefficients in the usual way. Accordingly, to predict the bulk acoustic properties of a fibrous material at elevated temperatures it is necessary only to measure these properties at room temperature, and then to apply the appropriate temperature corrections to the properties of the material flow resistivity and air when using the Delany and Bazley formulae.     

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.     

高平均功率开关晶体热力学特性有限元分析

基于有限元数值方法,就不同的光强分布模型以及电光晶体固定或自由的边界条件,模拟分析了KDP,DKDP,LiNbO3,BBO开关晶体材料在高平均功率激光负载下的热力学特性。结果表明:激光作用数s后,温升分布基本与光强分布一致;晶体表面的最大轴向位移和最大拉应力随光斑填充因子增大而增大;晶体的力学边界约束对最大轴向位移及最大拉热应力的影响随着光斑填充因子的增大而增强;在相同的入射激光光源及相同的边界条件下,KDP上的温升最大,热畸变最严重,DKDP次之,而LiNbO3和BBO具有较低的温升值或较低的热形变和热应力。     

A diamond anvil cell for the study of fluid mixtures at high temperatures

Abstract

A new diamond anvil cell has been developed to study the phase behavior of fluid mixtures at high temperature. Special care has been taken to achieve good temperature stability and small temperature gradients. Preliminar experiments show that the cell performs well.     

Optical encryption of gray-level image using on-axis and 2-f digital holography with two-step phase-shifting method

In this paper we propose an encryption/decryption technique of gray-level image information using an on-axis 2-f digital holographic optical encrypting system with two-step phase-shifting method. This technique reduces the number of holograms in phase-shifting digital holography and minimizes the setup of the encryption system more than multistep phase-shifting technique. We are able to get the complete decrypted image by controlling the K-ratio which is defined as the reference beam intensity versus the object beam intensity. We remove the DC-term of the phase-shifting digital hologram to reconstruct and decrypt the original image information. Simulation results show that the proposed method can be used for encryption and decryption of a 256 gray-level image. Also, the result shows some errors of the decrypted image according to K-ratio.     

Plasma etching of cavities into diamond anvils for experiments at high pressures and high temperatures

We describe a method for precisely etching small cavities into the culets of diamond anvils for the purpose of providing thermal insulation for samples in experiments at high pressures and high temperatures. The cavities were fabricated using highly directional oxygen plasma to reactively etch into the diamond surface. The lateral extent of the etch was precisely controlled to micron accuracy by etching the diamond through a lithographically fabricated tungsten mask. The performance of the etched cavities in high-temperature experiments in which the samples were either laser heated or electrically heated is discussed.     

固体材料低温热导率的测量

本实验以4.2K二级G-M制冷机为冷源,采用稳态轴向热流法测量了304不锈钢与环氧玻璃钢在低温下的热导率,讨论了样品上初始温差的成因及其影响,给出了热导率真实值所在的区间,并对测量误差以及各种漏热带来的影响进行了分析。     

Numerical simulation of transconductance of AlGaN/GaN heterojunction field effect transistors at high temperatures

Based on the investigation of the influence of temperatures on parameters, including polarization, electron mobility, thermal conductivity, and conduction band discontinuity at the interface between AlGaN and GaN, the temperature dependence of transconductance for AlGaN/GaN heterojunction field effect transistors (HFETs) has been obtained by using a quasi-two-dimensional approach, and the calculated results are in good agreement with the experimental data. The reduction in transconductance at high temperatures is primarily due to the decrease in electron mobility in the channel. Calculations also demonstrate that the self-heating effect becomes serious as environment temperature increases.