Mars Observer Laser Altimeter: laser transmitter

The Mars Observer Laser Altimeter utilizes a space-qualified diode-laser-pumped Q-switched Nd:YAG laser transmitter. A simple numerical model of the laser energetics is presented, which predicts the pulse energy and pulse width. Comparisons with the measured data available are made. The temperature dependence of the laser transmitter is also predicted. This dependence prediction is particularly important in determining the operational temperature range of the transmitter. Knowing the operational temperature range is especially important for a passive, thermally controlled laser operating in space.     

简易估计激光探测系统作用距离

为了测试评估激光探测系统的有效作用距离,基于室内大气激光传输过程模拟,本文提出一种简易估计激光探测作用距离的方法,分析了大气传输的特性及室内模拟实现方法,模拟搭建了激光探测系统并对其进行了室内试验测试和外场实地验证,得到了一些有益参考数据,针对室内.外场试验数据偏差现象,定性分析了误差影响因素.试验结果表明,该方法简单、可行,可简易估计激光探测系统的作用距离,为外场测试提供参照范围,增强外场测试针对性进而提高测试效率,为测试评估激光探测系统作用距离提供了有益参考.     

Correlation measurements using clipped laser speckle

Clipped laser speckle is used to measure the correlation of time-varying laser speckle. As with standard intensity correlation, clipped speckle is correlated to determine the magnitude of the correlation coefficient. The simple nature of clipped speckle permits high-speed measurements of correlation and velocity. A closed form approximation to the clipped correlation function valid for arbitrary clipping thresholds is presented. The approximation is used to make correlation measurements on speckle from a rotating diffuser using a 2-D random access detector array.     

Studies for Laser Densification of Ceramic Coating

A mathematical analysis describing the densification of ceramic coating processed with a moving TEM₀₀, mode laser beam has been presented in this paper. Calculations of the depth of the heat affected zone in ZrO₂, A1₂O₃ and TiO₂ ceramic substances is performed by adopting a three-dimensional quasi-steady state heat conduction model based on the mechanism of viscous solid-phase densification. Also, a working range for these ceramics coating densification is predicted by varying the laser beam power, spot size and scanning velocity. The heat-affected layer in ZrO₂ compact is found to be confined within a depth of 50 μm from the surface and it is fully densified for grains of initial radius 5 μm. A simple expression for temperature distribution is presented, which is found to provide sufficiently accurate estimates within a limited region around the laser spot.     

The Generation of a Dense Hot Plasma by Intense Subpicosecond Laser Pulses

A simple model is developed for describing the interaction of intense femtosecond laser pulses with solid-state targets which is based on a set of equations of two-temperature hydrodynamics for electrons and ions of a plasma formed upon ionization of the target matter, equations describing the variation of ion composition of plasma upon ionization and the heat energy expenditure on thermal ionization, and equations defining the energy contribution by laser radiation to the target matter. A self-similar solution is suggested which well describes the heating of plasma electrons during the time of effect of a femtosecond laser pulse in a wide range of its parameters. Lagrangian computer codes developed for this purpose are used to derive, in a one-dimensional approximation, a numerical solution for the set of equations for the parameters corresponding to femtosecond experimental facilities under development in Germany and Russia. Profiles of hydrodynamic quantities (electron and ion temperature, plasma pressure and density, mean ion charge) obtained in the numerical solution at different moments of time may be used for preliminary assessment of the results of future experiments with a view to optimizing their parameters.     

Laser diode facet modal reflectivity measurements

A simple and accurate method for measuring the front facet modal reflectivity of a Fabry-Perot laser diode is presented. In this method, optical feedback from an external mirror of known reflectivity, R(ext), is used to alter the laser diode threshold current. The effect of the external mirror and front facet reflectivities on the threshold current then allows for a measurement of the front facet modal reflectivity of the laser diode and is theoretically and experimentally studied. This method was used to measure a facet reflectivity of R(2) = 0.0151(+0.0018/-0.0032) [R(2) = 0.00592(+0.00085/-0.00123)] for a commercially antireflection-coated facet of a laser diode with a center wavelength of 795 nm (935 nm). The results of the reflectivity measurements based on the threshold current as a function of the external mirror reflectivity are compared with the results of the reflectivity measurements based on modulation depth of the optical spectrum [IEEE J. Quantum Electron. QE-19, 493 (1983)].     

Transient Radiative and Conductive Heat Transfer in Ceramic Materials Subjected to Laser Heating

In this work the problem of transient energy transport in a conductive, emitting, and scattering medium is addressed. A new approach for describing the transient response of a participating one-dimensional layer subjected to a finite laser pulse is presented. The model considers heat transport in one dimension by conduction and radiation, where the radiative field is described by the two-flux approximation. The material is assumed to be gray, homogeneous, and isotropic, with physical and optical properties dependent on temperature. Numerical results have been obtained on a layer of low optical thickness using the thermophysical properties of zirconia as a typical material. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6-8, 2004, Orléans, France.     

基于FPGA的逐次逼近算法实现激光干涉信号细分

为了实现激光干涉测量中信号的高速度、高精度细分,对正切细分算法中的除法运算进行了改进,采用逐次逼近算法替代使用较多的移位相减算法。实验证明逐次逼近算法比移位相减算法运算速度更快、资源占用较少。更适合FPGA信号细分高速度、高精度要求。     

YAG Laser End and Side Pumped by a Laser Diode

A combined end and side pump approach for a YAG laser pumped by a laser diode is proposed. The theoretical analysis of the total pump efficiency of the end and side pump module is presented. A laser-diode-pumped YAG laser is successfully demonstrated by use of this pump configuration. The experimental pump threshold is 81.2 mJ, the maximum output is 4.4 mJ, and the optical efficiency is approximately 3.1% for Q-switched operation of the YAG laser.     

Laser welding

A brief state-of-the-art review of laser welding has been presented. Results of our experimental studies on laser welding of Ti-6Al-4V have been reported. Results of weld evaluation including microstructure, mechanical properties and microchemistry have also been presented.     

High Repetition Rate,High Average Power Er:YAG Laser at 2·94 μm

Abstract

A simple kinetic model is presented which describes the temporal behaviour of an Er:YAG laser pulse and predicts c.w. operation. The use of transfer dye to selectively pump the erbium ions, and suitable optimisation of laser cavity parameters has allowed operation up to 40Hz with 4W average power. 10W at 100Hz is predicted.     

Range-dependent Optical Feedback Effects on the Multimode Spectrum of Laser Diodes

Abstract

Weak optical feedback from diffusely-reflecting objects can dramatically affect the optical spectrum of homogeneously-broadened laser diodes operated near the lasing threshold. Switching between two or more oscillation modes can be controlled by as little as 1 nW of optical feedback power. The modulation effects on the optical spectrum and total power output depend on the phase of the returned light, and the strength of the effect has a range dependency that is useful for metrology applications. In the present work, experimental and theoretical analyses of these phenomena are presented, and a simple metrology tool for position sensing and remote surface profiling is proposed.     

便携式激光表面粗糙度测量仪

介绍了一种基于光散射原理的便携式激光表面粗糙度测量仪。它采用半导体激光器光源，以元心光路结构接收、处理经粗糙表面调制的散射光带，成功地解决了粗糙度测量精度高低与测量范围大小相矛盾的问题。仪器结构简单、操作方便、测量效率高，精度能满足生产实际的需要。     

光纤传感器系统中激光光强波动的特性及其补偿技术

本文针对He-He激光器的光强波动问题提出了一种新方法。在该方法中,光源输出的变化并没有得到抑制或控制,但可以消除它对测量结果的影响。结合和使用分光技术与微机技术,并建立了一相应系统。该系统结构简单可靠,它用于微位移和粗糙度测量系统中,获得了满意的效果和较高的精度。     

偏振激光在大气传输中的退偏研究

用蒙特卡罗方法对偏振激光在浓雾和弱雾中的传输特性进行建模。当偏振激光波长相同时,分别分析计算了偏振激光在浓雾和弱雾中不同雾气粒子半径下传输的退偏特性。并比较了偏振激光在不同传输距离时,其偏振角的变化情况。仿真结果表明：1）雾粒子半径较小时,偏振角变化最大的主要集中在后向,而前向整体上的偏振角很小,球形粒子的单次前向散射偏振角是不变的;2）随着雾粒子半径的增大偏振角出现了越来越多的复杂旁瓣;3）光散射偏振角随着光传输距离的增加而增大,并且在浓雾中传输比在弱雾中传输的退偏大。     

Simple Approximate Theory for Twin-guide Fabry-Perot Laser Amplifier Switches

Abstract

A simple modal analysis is presented of twin-stripe semiconductor Fabry-Perot laser amplifier switches that operate via simultaneous changes in gain and refractive index due to free carrier injection. The analysis of Adams [3], based on weak coupled mode theory, is first briefly reviewed, and compared with the modal method. An approximate solution is then derived, which shows good agreement with the full theory. Approximate resonance and lasing conditions are also found, and limiting values for switch crosstalk are estimated.     

Laser rockets

The results of experimental and theoretical investigations of the dynamic characteristics of a laser rocket in the initial flight path segment are presented. The energy to a laser jet propulsor was delivered with the beam of a CO-or CO₂-pulsed laser with a pulse energy ranging from 0.1 to 3.0 kJ at a repetition frequency of 100 Hz.     

一种激光起爆系统检测技术

介绍激光起爆系统的主要构成及研究进展,针对激光起爆系统检测的难点,提出了一种简单、可行的检测方法。该文重点进行了激光起爆系统的外置式检测技术研究,包括激光起爆器的光路设计、检测光纤设计和耦合结构设计,并通过试验验证,解决了激光起爆器光路定量反射的问题,可为武器、航空航天等高可靠系统提供一定借鉴。     

Consideration of the Effect of Instability of the Laser Emission Power on the Final Result of the Reproduction of the Unit of Mean Laser Emission Power and the Transmission of Its Dimensions

An algorithm for reconstructing the form of continuous laser emission at the input of a system for measuring the standard of the unit of mean laser power is presented. The power can also be calculated using this algorithm.