转拍白光再现全息肖象的研究

本文介绍了我们在转拍白光再现的全息肖象方面的研究工作.讨论了拍摄工作中所需要特别注意的若干问题.如:参物光束比的选择、肖象尺寸大小的估算、视角的估算、获得高衍射效率的化学处理的方法、获得高信噪比的化学处理的方法等.     

模压全息图母版的拍摄研究

目前拍摄模压全息母版用的记录材料都是光刻胶.本文从它本身的特点(灵敏度低,浮雕型相位光栅和拍摄对象是散射物体等)出发,指出要拍摄出质量好的光刻胶母版应当注意到的问题.诸如拍摄参数的选择应同时考虑到衍射效率和信噪比、照明的均匀性问题、逆共轭光再现、消偏振、相干长度、外界振动对拍摄的影响问题.通过分析表明高质量的全息图不可能靠延长曝光时间来获得,使用相干性好的大功率激光束来拍摄,是非常有必要的.     

浮雕型全息相位光栅的衍射

本文从理论上推导出了浮雕型相位全息光栅所满足的衍射方程式,并数值计算了光刻胶四种情况下的+1级衍射光的衍射效率与相位光栅刻蚀深度的关系.还和大量实际拍摄的全息光栅作了比较,发现它基本上都能与实验相符；文中还指出了如何选择拍摄参数来控制光栅的刻蚀深度,以确保制作高衍射效率和高信噪比的PET(聚酯薄膜)模压全息片所需要的光刻胶母版拍摄.     

超短脉冲激光选通电子学全息成象系统研究

本文介绍了最早到达光概念,分析了超短脉冲激光电子学全息实现选通最早到达光成象的原理.用超短脉冲激光拍摄全息图,相当于用多色光记录全息图,当用单色光再现这种全息图时,会给再现象造成一个模糊量.在一般全息理论中,只讨论了采用单色光记录全息图,复色光再现所造成的模糊量.因此,本文中讨论的是一个与此相反的问题,即用多色光记录全息图,单色光再现的情况,并且着重讨论了超短脉冲激光记录全息图的情况.最后得出结论,在用超短脉冲激光拍摄全息图时,最好采用象面全息术.     

全息显示技术讲座 第六讲 其他全息显示方法

<正> 全息显示是全息术发明以来所取得的最卓有成效和最重要的应用之一.前五讲,我们介绍了适合于显示用的各种全息图:透射和反射菲涅耳型全息图、象全息图、傅里叶变换全息图和彩虹全息图,并概述了全息显示的重要成果——合成全息和全息电影.这一讲介绍其它全息显示方法,从中可进一步看到全息显示的广阔前景。一、深度多路合成全息第五讲中,介绍了角度多路合成全息,即从一系列不同角度拍摄的物体二维照片综合成一张全息图,可以再现原来的三维物体。这里,我们介绍另一种合成全息——深度多路合成全息。它是从一系列不同深度拍摄的二维照     

超短脉冲激光选通电子学全息成象系统研究

本文介绍了最早到达光概念，分析了超短脉冲激光电子学全息实现选通最早到达光成象的原理．用超短脉冲激光拍摄全息图，相当于用多色光记录全息图，当用单色光再现这种全息图时，会给再现象造成一个模糊量．在一般全息理论中，只讨论了采用单色光记录全息图，复色光再现所造成的模糊量．因此，本文中讨论的是一个与此相反的问题，即用多色光记录全息图，单色光再现的情况，并且着重讨论了超短脉冲激光记录全息图的情况．最后得出结论，在用超短脉冲激光拍摄全息图时，最好采用象面全息术．     

体积全息衍射效率的分析

本文指出对于通过折射率变化来实现相位调制的全息图(无论是漂白后的银盐干版,或DCG版),在通常情况下其相位调制度都较小,不可能发生过调制现象,故拍摄参数选择范围相对较宽。要获得高衍射效率全息照片的关健应放在如何提高干涉项引起的相位调制折射率n₁上。本文还指出当反射全息处於弱布喇格衍射的情况下,再现图象的单色性下降,并存在透射象。     

全息术诊断激光产生蒸汽羽等离子体

介绍了用脉冲激光全息二次曝光法诊断Q开关钕玻璃激光脉冲与LY12铝靶(φ50×3)耦合产生蒸汽羽等离子体的原理和实验。在打靶激光脉宽约50ns,功率密度约5GW/cm~2条件下,拍摄了激光产生蒸汽羽等离子体的全息干涉图。运用Abel变换和Saha方程,对全息干涉图进行数据处理,得到对激光与物质相互作用机理研究的有用参数。     

用预泵浦技术实现Cr4+、Nd3+双掺YAG激光器自调Q可控输出

对LD泵浦Cr⁴⁺、Nd³⁺双掺YAG自调Q激光器进行了研究,在连续泵浦和脉冲泵浦下获得了1.064μm调Q偏振激光脉冲输出,脉冲宽度(FWHM)为30ns,单脉冲能量为0.5μJ.采用直流预泵浦技术使Q开关时间的不确定度从×10ms减小到5μs左右,并使激光Q脉冲重复率从1kHz提高到近17kHz,该方法也同样适用于其它被动调Q激光器.     

钛宝石激光再生放大器的研究

最近,我们采用上海光机所生产的(5.2×5.5×10)mm 的钛宝石激光晶体作为再生放大器的激光介质,实现了钛宝石激光再生放大器的运转.获得了1.2mJ 的能量输出.再生放大器的泵浦源是调 Q 的倍频 Nd:YAG 激光器,它的输出光脉冲宽度小于10ns,脉冲重复频率为10Hz,实验中为避免损伤晶体,采用的泵浦能量为50mJ.种子脉冲来自于自锁模钛宝石激光器,种子脉冲首先经过光栅展宽后再注入到再生脉冲,然后进行放大.注入的种子脉冲能量为1nJ,再生腔为平凹腔,R 为4m,腔长为1.65m.再生放大器的实验结果如图所示.     

Transient vibration measurements using multi-pulse digital holography

An optical system for the evaluation of transient deformations will be described. In order to increase the temporal resolution, a ruby laser producing four pulses has been used. Four separate digital holograms (one hologram for each pulse) of the test object are recorded in a few microseconds on three CCD sensors. The Fourier method is used for the quantitative evaluation of the digital holograms. The phases are obtained from the complex amplitudes, and the deformation at different times is calculated from phase subtraction. Experimental results are presented.     

High speed holocinematography using spatial multiplexing for image separation

Up to eight holograms are successively recorded at maximum repetition rates of 20kHz. A multiply Q-switched ruby laser is used to produce the series of coherent light pulses for hologram exposure. All holograms are recorded on the same plate. Image separation of different holograms is achieved by spatial multiplexing using a rotating disk with apertures directly in front of the holographic plate. The performance of the technique is demonstrated by reconstructions of a hologram series taken of laser produced cavitation bubbles following optical breakdown in water.     

A new holographic measurement of frequency sweeping of the output from a Q-switched ruby laser

The frequency sweep of the output from a Q-switched ruby laser is investigated by using a holographic technique of a moving object. The chirp rate of the frequency sweep is assumed to be linear in time. We also propose how to measure in a single-exposure hologram the temporal coherence of the same laser.     

Numerical calculations of intracavity dye Q-switched ruby laser

A mathematical model describing the dynamic emission of the Q-switched ruby laser has been adapted. The suggested model allows the investigation of the effects of a dye cell on the mode characteristics of the ruby laser and, moreover, the study of the effect of the laser input parameters on the output laser pulse. This model simulates the nonlinear effects of dye pulse modulation on the laser emission.In addition, a numerical solution of a nonlinear rate equation system of the adapted model is discussed. The solution estimates the density of the emitted radiation, population inversion and energy transfer processes of the ruby laser rod and dye cell for different emission regimes (one pulse regime, free running pulses, repetition periodic pulses). The estimated results of the laser output pulse characteristics are in a good agreement with the other calculated and experimental results.     

Tunable high order stimulated Raman-anti-Stokes radiation produced by light mixing

High order anti-Stokes Raman spectral lines can be produced by irradiation of liquid nitrogen with the focused beam of a giant pulse ruby laser. By mixing the ruby light with that of a tunable dye laser tunable anti-Stokes lines have been produced. These lines are not observed if the ruby laser beam is blocked off.     

Design and fabrication of an optimum holographic optical element lens for a femtosecond laser pulse using a hologram computer-aided design tool

Design and fabrication of an optimum holographic optical element (HOE) lens for a femtosecond laser pulse using a hologram computer-aided design (CAD) tool is presented. The hologram CAD tool, which the authors have developed can design, analyze, and evaluate holograms fabricated by interferometrical technique. The function of the tool is extended to design and analyze a HOE lens illuminated with a femtosecond laser pulse. An optimum HOE lens for a laser pulse, which has 130 fs duration, 720 nm central wavelength, and 10 nm spectrum bandwidth, is designed by the tool. The optimum HOE lens gives both high diffraction efficiency and small amount of aberration. The designed HOE lens is fabricated and its optical characteristics have been experimentally evaluated. The reconstructed point images agree with the results of the numerical simulations by the tool. The tool demonstrates the capability of designing the optimum HOE lens for a femtosecond laser pulse.     

Temperature field of a ruby laser

Formulas describing the temperature fields of a ruby laser cooled in various ways are derived. The laser can operate either as a single pulse generator or as a source emitting free-generation pulses at a specified frequency. The resulting formulas are used to compute the heating and cooling of the active medium of the ruby laser.     

The effect of saturable absorber lifetime in picosecond pulse generation. II. The cresyl-violet laser

Picosecond pulse generation in a pulsed cresyl-violet laser, mode-locked by four saturable absorbers (DTDCI, DDCI, DCI, and DCI'), of different relaxation times, has been directly studied. In contrast to the ruby laser case, the ultimate pulse duration is largely independent of the absorber lifetime. Pulses of ? 4 psec duration are obtained from a cw Rhodamine B dye laser mode-locked with cresyl-violet.     

Operation of a high power,broadly tunable infrared dye laser

We discuss the operation and performance of a ruby pumped infrared dye laser with a wide tuning range and a high out-put power. The longitudinally pumped infrared laser was operated in the Littrow configuration without an intracavity beam expander. The dye, IR 125, exhibited a tunability range that extended from 8325 Å to 9375 Å. The dye laser had a pulse duration of 20 ns and an output power of 12.5 MW with a 2.3 joule ruby pump. The maximum output power of the infrared laser was limited by the damage threshold of the tuning element.     

Temporally Resolved Spectroscopy of Laser-Induced Carbon Ablation Plasmas

Temporally resolved emission spectra (360-630 nm) of carbon ablation plasmas produced during laser hole boring by a 25-ns duration 1-J ruby laser pulse are presented. The emitted line radiation originates from, C+++ to C+ depending upon the time relative to the laser pulse. Plasma temperatures of 12-14 eV during the laser pulse to about 4 eV, 140 ns after the laser pulse are obtained by comparing the spectroscopic results to a collisional-radiative equilibrium (CRE) model which bridges the gap between the local thermodynamic equilibrium (LTE) model and the coronal model.