2007年激光市场和技术

本文叙述了2007年激光市场及相关的技术状况.2007 年的激光市场规模预计为60亿美元,比去年增加8%.半导体激光器的销售额占总数的一半以上.半导体激光器的主要应用是光学数据储存和长途光通讯.非半导体激光器具有比较强大的激光能力和广泛的应用,但是比较复杂.非半导体激光器主要用于与半导体及汽车商业有关的材料加工.非半导体激光器的第二个用途是与整容化妆有关的医学治疗.光纤激光器是最有魅力的非半导体激光器.     

激光陀螺反射镜散射检测方法

闭锁效应是影响激光陀螺性能的重要因素,而光束在反射镜表面反射时的背向散射则是形成闭锁效应的主要原因。基于矢量叠加理论,对激光陀螺反射镜背向散射对谐振腔总背向散射的影响进行了分析。在此基础上,提出一种反射镜散射的在线测量方法,以半导体激光器为光源构成远心光路,通过显微镜收集散射光,并利用CCD记录反射镜膜面的散射光场。根据散射图样对反射镜进行筛选,并最终确定反射镜膜面的安装位置与方向。在某型激光陀螺上进行了实验,结果表明使用该方法选配可以将锁区合格率由原来的75%提升至95%,改进效果明显。该检测方法结构简单,可有效控制由反射镜散射引起的锁区超标问题,在激光陀螺反射镜的在线检测及激光陀螺装调方面有很好应用前景。     

前言

激光是一种方向性好,能量高度集中,具有单色性和相干性的新型光源。第一台激光器——红宝石激光器,是1960年出现的。以后经过几年的摸索和普查,很快就发现了固体、气件、半导体等各类工作物质。      

基于高斯相位调制的半导体激光器线宽展宽方法

基于激光器驱动的干涉型光纤陀螺是近年来国内外光纤陀螺研究的新热点,但半导体激光器作为一种窄线宽的高相干光源,将其用于干涉型光纤陀螺又会重新引入瑞利散射、Kerr效应和偏振交叉耦合等非理想特性进而影响陀螺的精度,因此有必要将半导体激光器的线宽加宽后再使用。为实现半导体激光器的线宽展宽,建立了基于高斯相位调制的光谱展宽卷积模型,利用OptiSystem仿真分析验证线宽展宽效果;通过搭建光路进行实验验证,实验结果证明,通过所提出的展宽方法可以将线宽10 MHz的激光器的光谱展宽成线宽11 GHz的光谱。为干涉型光纤陀螺中半导体激光器的应用提供了基础保证,具有一定的工程应用价值。     

激光超声无损检测

本文介绍自行研制的非接触式激光超声激励和检测系统，采用共焦式法布里—珀珞干涉仪实现对纳米量级微幅单次超声窄脉冲的检测，并应用该系统进行激光超声探伤及测定材料弹性常数的研究，实验结果表明激光超声技术是有效而且实用的     

激光陀螺谐振腔损耗与相位差测量

介绍了激光陀螺谐振腔损耗及相位差的一种测量方法。将频率可调激光器发出激光入射被研究激光陀螺谐振腔，使之产生强迫振荡。用光电接收器接收振荡功率信号，输入计算机分析，绘出谐振腔的功率谱线图。通过测量谱线半波宽度、纵模间隔时间兀计算出谐振腔的损耗及相位差。损耗测量精度可达10^-6级，相位差测量精度达0．1度。     

激光聚焦击穿液体的爆炸气泡特性

高功率激光聚焦击穿液体介质,类似于聚焦区域发生了微爆炸.研究了激光聚焦击穿爆炸与水下微爆炸之间的相似性.采用高功率脉冲激光器、光学聚焦系统、高速摄像、测量水听器建立了激光击穿爆炸源的产生及爆炸气泡、爆炸声波特性测量系统.对不同参数激光聚焦击穿水、酒精、硅油等粘性液体,观测到了激光击穿爆炸冲击波、气泡脉动、气泡压缩冲击波...     

一种确保激光陀螺低温启动的辅助启辉方法

激光陀螺在低温下启辉电压过高,严重影响了其工程应用。为了确保低温下陀螺可靠启动,借鉴激光器领域内的预电离技术,提出一种激光陀螺辅助启辉方法。在陀螺谐振腔阴极附近放置一个辅助启辉发光装置,发射高能量光束照射陀螺谐振腔阴极内表面,增加阴极的次级电子发射能力,可以有效降低陀螺辉光放电电压。分别利用紫外气体发光管和紫外波段半导体发光二极管作为光源进行了陀螺启辉电压对比试验,结果表明:低温下两种光源均可有效降低陀螺启辉电压,但两者降低启辉电压的效率有差异,紫外灯效率在5%～30%之间,紫外波段的半导体发光二极管的效率在12%～28%之间,前者降低电压离散性较大,后者较为均匀,综合看,后者效果更为显著。     

电子束激光器

引言高功率大能量激光器是现代激光器研究的一个重要方向。其可能的长远应用是:直接摧毁目标的激光热武器——激光炮;受控聚变点火的所谓超级激光;实现远距离无线辐射传输动力。正因为这些重大项目应用的可能性,美苏等国都花费大量经费进行研究。达到这些应用目标的主要手段有四种:1.固体釹玻璃激光器,2.气体动力激光器,3.化学激光器,4.放电气体激光器。      

用PVDF实时测量激光诱导的冲击波压力

本文用自己研制的ＰＶＤＦ（ｐｏｌｙｖｅｎｙｌｉｄｅｎｆｌｕｏｒｉｄｅ）压电传感器测量了０．２ｍｍ厚铝和２．０８ｍｍ厚Ｔ３００／环氧复合材料中激光诱导的冲击波压力，首次获得了这些材料中激光冲击波压力的时间演化波形。实验在中国科大强激光实验室的ＹＡＧ脉冲激光器上进行，激光波长１．０６μｍ，脉宽３３ｎｓ，靶面平均功率密度为１０９Ｗ／ｃｍ２量级。从所得数据估计了表面入射压力，其值与已有结果符合良好。实验结果证实，ＰＶＤＦ压电传感器频响高，量程宽，多次使用重复性好，可有效应用于激光冲击波压力的实时测量     

构建相干长度之外的激光干涉仪

用于微型光刻技术中的多数紫外线（UV）或深紫外线激光器，无论是基于气体的准分子或二极管泵浦固态（DPSS）激光器，其输出频谱均较宽。与此同时，能传送紫外或深紫外光的多数光学材料均具有较高度频散性（即它们的折射率，n（λ），随波长λ变化）。在这种情况下构建一台紫外干涉仪比那拥有狭窄光谱的激光和几乎恒定折射率的光学材料的情况要复杂得多。本文描述一项激光干涉技术，据此可以补偿光学材料的高频散性，从而构建传统意义上所定义的相干长度之外的激光干涉仪。给出理论上的陈述，并提供初步实验结果。本文最后讨论了此情况下干涉条纹的对比度、激光相干长度，以及如何控制光源的时域不稳定性和空间不均匀性的方法。     

微光学陀螺仪系统结构的研究

介绍了谐振型和干涉型两种微光学陀螺仪的分辨率计算公式,并在光纤仿真装置上,分别进行了系统结构的实验研究.在谐振型装置中,作为光源采用了具有 Bragg 光栅的窄线宽激光二极管.在干涉型装置中,为了保证双向光束在Sagnac 效应敏感环 (SSR) 中可以循环传播,采用了大功率的超辐射发光二极管(SLD)作为光源.为了保持双向光束在 SSR 中循环传播多圈,需要在 SSR 中插入一个光放大器,以补偿光束在传播中的各种损耗.研究结果表明,所建议的系统结构对于开发中等精度的微光学陀螺仪产品具有可行性.     

New technique for multi-component flow velocity measurements using a single HF-pulsed diode laser and a single photodetector

The reduction of components and enhancement of signal-to-noise ratio are main advantages of a high-frequency pulsed multi-component LDA. Two or three high-frequency pulsed diode lasers are still required if two or three velocity components are measured. In this paper a new technique has been proposed and experimentally verified, which allows one to take advantage of the peak power enhancement by the pulsing technique and to use a single high-frequency pulsed diode laser for multi-component flow velocity measurements. The practical realizations of this technique using fibre optics and integrated optical devices as a miniaturized multi-component LDA are described.The work presented in this paper was partly supported by the Deutsche Forschungsgemeinschaft (DFG) under contract No. DO 292/1-4     

Laser and avalanche diodes for velocity measurement by laser Doppler anemometry

The paper describes the possibilities of using semiconductor components for laser Doppler anemometers. This includes laser diodes D at the transmitting optics and PIN and avalanche diodes at the receiver. The advantages and disadvantages of various laser diode types are described, reference is made to problems such as focussing and wavelength stabilization and practical hints are given for the use of LDA. Extensive measurements of the attainable signal-to-noise ratios (SNR) of photomultipliers and of a number of photodiodes of different make have shown that some photodiode models are now superior to photomultipliers. Laser diodes should be used together with photodiodes to construct miniaturized laser Doppler anemometers, as such semiconductor LDA are much more efficient than conventional anemometers with gas lasers and photo-multipliers. Moreover, miniaturized LDA designs can now also be used for battery operation and field application.     

超燃燃烧室气流参数诊断

基于可调谐二极管激光器吸收光谱技术, 利用7185.597cm^{-1}, 7444.35cm^{-1} + 7444.37cm^{-1}(重合吸收线)两条H_2O吸收线, 采用分时扫描-直接探测策略组建多光路吸收测量系统, 在4kHz的测量频率下, 定量测量了燃烧室气流的静温、水蒸气浓度和流向速度. 利用位移机构, 在以C_2H_4为燃料的超燃直连式试验台中, 在单次试验中同时诊断燃烧室内某截面和燃烧室出口的多气流参数的截面分布. 利用燃烧室出口截面的水蒸气浓度分布, 并结合壁面静压计算燃烧效率; 利用燃烧室出口截面的静温和速度分布, 获得出口气流马赫数分布; 利用凹腔后部某截面的温度和水蒸气浓度分布, 判读了凹腔附近流场特征.      

Towards laboratory produced relativistic electron–positron pair plasmas

We review recent experimental results on the path to producing electron–positron pair plasmas using lasers. Relativistic pair-plasmas and jets are believed to exist in many astrophysical objects and are often invoked to explain energetic phenomena related to Gamma Ray Bursts and Black Holes. On earth, positrons from radioactive isotopes or accelerators are used extensively at low energies (sub-MeV) in areas related to surface science positron emission tomography and basic antimatter science. Experimental platforms capable of producing the high-temperature pair-plasma and high-flux jets required to simulate astrophysical positron conditions have so far been absent. In the past few years, we performed extensive experiments generating positrons with intense lasers where we found that relativistic electron and positron jets are produced by irradiating a solid gold target with an intense picosecond laser pulse. The positron temperatures in directions parallel and transverse to the beam both exceeded 0.5 MeV, and the density of electrons and positrons in these jets are of order 10¹⁶ cm⁻³ and 10¹³ cm⁻³, respectively. With the increasing performance of high-energy ultra-short laser pulses, we expect that a high-density, up to 10¹⁸ cm⁻³, relativistic pair-plasma is achievable, a novel regime of laboratory-produced hot dense matter.     

Accelerating piston action and plasma heating in high-energy density laser plasma interactions

In the field of high-energy density physics (HEDP), lasers in both the nanosecond and picosecond regimes can drive conditions in the laboratory relevant to a broad range of astrophysical phenomena, including gamma-ray burst afterglows and supernova remnants. In the short-pulse regime, the strong light pressure (>Gbar) associated ultraintense lasers of intensity I > 10¹⁸ W/cm² plays a central role in many HEDP applications. Yet, the behavior of this nonlinear pressure mechanism is not well-understood at late time in the laser–plasma interaction. In this paper, a more realistic treatment of the laser pressure ‘hole boring’ process is developed through analytical modeling and particle-in-cell simulations. A simple Liouville code capturing the phase space evolution of ponderomotively-driven ions is employed to distill effects related to plasma heating and ion bulk acceleration. Taking into account these effects, our results show that the evolution of the laser-target system encompasses ponderomotive expansion, equipartition, and quasi-isothermal expansion epochs. These results have implications for light piston-driven ion acceleration scenarios, and astrophysical applications where the efficiencies of converting incident Poynting flux into bulk plasma flow and plasma heat are key unknown parameters.     

气流化学激光理论研究的若干进展

以超声速HF/DF化学激光和超声速氧碘化学激光(COIL)为代表的气流化学激光(GCL), 因其科学意义、军事和工业应用价值，近30多年来得到了突飞猛进的发展.由于超声速膨胀混合流在控制强放热反应动力学和热力学过程方面的特殊本领，使气体动力学在高功率GCL的发展中起着关键性的作用.高功率GCL性能的分析计算自然也沿用非平衡气体动力学的方法，假定气流(包括激光能级分子和原子)为连续介质，谱线为均匀加宽，并联立求解气体动力学方程组，增益动力学和基于光强迭加原则的辐射传输诸方程，称为速率方程(RE)模型.20世纪70年代后期又提出和发展了GCL性能计算的半气体动理学(SGK)模型，在SGK模型中仍假定气流为连续介质，但同时考虑了激光能级分子微观热运动的贡献，谱线加宽的非均匀加宽效应，并用双参数摄动法求解激光能级分子速度分布函数方程组(即广义Boltzmann方程组), 因此SGK模型是一个同时考虑宏观和微观尺度运动的跨尺度模型.本文综述RE模型和SGK模型以及用它们预测GCL性能的若干研究进展，同时简评等增益模型和腔模(模图样)理论研究的一些进展.最后从气体动力学的角度提出一些值得 进一步研究的课题.     

Comparison measurements for selection of suitable photodetectors for use in Nd: YAG LDA systems

Laser-diode-pumped Nd:YAG lasers (=1064nm) are compact, single-transverse mode laser sources with a higher output power than diode lasers ( 800 nm). They are suitable light sources for miniaturized laser Doppler anemometer systems. On the other hand, the sensitivity of conventional detectors and the scattering efficiency particularly of particles smaller than 1 m are reduced, when these light sources are used. The paper describes comparison measurements of commercial photodetectors based on Si, Ge and InGaAs in a test LDA with an Nd:YAG laser. The achievable signal-to-noise ratios (SNR) of the Doppler bursts versus the laser power in the measuring volume are compared. This shows that Silicon Avalanche photo diodes (APD) for the near-infrared using a special technology and InGaAs-APDs with low-noise pre-amplifiers can be used advantageously.Similar comparison measurements with an LDA system at =830 nm show that an Nd:YAG laser based LDA is more sensitive and leads to higher SNRs because of its higher output power, even though the Mie scattering efficiency and the detector sensitivity are reduced.     

The optical properties of the laser beam passed through a turbulent shear layer

The related fluid dynamic theory, experimental device and some preliminary results of the study of the optical properties of a laser beam passed through a turbulent shear layer are presented. The method of image processing for the determination of the optical density from a interferogram by means of a Microneye Bullet and a Microcomputer is also described.