基于激光点云数据的地形地貌测量研究

针对在实际测量地形地貌时激光数据过滤误差较大的问题,设计了基于激光电云数据的地形地貌测量及处理方法。采集激光点云数据,结合公共标靶法与最小二乘法补全点云数据且自动过滤非地面数据,对激光点云数据的平面坐标与高程实施转换,生成待测区域的地形地貌等高线,实现该区域的地形地貌测量。通过实验验证设计方法性能,结果表明,该方法可实现分散站点激光点云数据的拼接与过滤处理,过滤性能稳定且过滤误差较低,平均为2.1%,可精准测量实验地区的地形地貌,坐标值误差平均为0.187,满足实际应用中的地形地貌高精度测量需求。     

Dynamic characteristics of bistable laser diodes

A stability analysis of bistable laser diodes, which gives a first analytical explanation of the recently observed high-speed bistable switching and self-pulsation, is presented by introducing two key parameters. It is shown that switching and self-pulsation are associated with two time scales. Turn-on and turn-off dynamics can be characterized by two different sets of eigenvalues which are used to analytically explain the switch-off and switch-on transients observed in experiments. It is also shown that the gain function profile can significantly affect the performance of self-pulsation operation of bistable laser diodes. The analysis also proves that the existence of two critical points has an important effect on the switching time if switching occurs around one of them. The results of the present analysis agree well with those of an exact numerical simulation. In addition, the analysis can be applied to study dynamic characteristics of a bistable laser diode (BLD) with other more complicated structures such as distributed feedback (DFB) laser diodes, multiquantum-well (MQW) laser diodes, etc     

可调谐半导体激光吸收光谱甲烷浓度监测系统

以中心波长为1 650 nm的激光光源作为探测光源,并结合波长调制光谱以及谐波探测技术,设计了一套基于TDLAS(可调谐二极管激光吸收光谱)技术的CH4气体浓度探测系统.结合长光程测量池,以浓度为99.999%的高纯N2为背景气体,对8种浓度的CH4气体进行了测量,利用配置的101×10-6 CH4气体对系统进行了稳定...     

Toward single-cycle laser systems

Few-cycle pulse generation based on Ti:sapphire, Cr:forsterite, and Cr:YAG gain media is reviewed. The dynamics of these laser systems is well understood in terms of soliton and dispersion managed soliton formation stabilized by artificial saturable absorber action provided by Kerr-lens modelocking. These systems generate 5-, 14-, and 20-fs pulses with spectral coverages of 600-1150, 1100-1600, and 1200-1500 nm, respectively. The design of dispersion compensating laser optics providing high reflectivity and prismless operation over this bandwidth is discussed. A novel active synchronization scheme based on balanced optical cross correlation, the equivalent to balanced microwave detection, for synchronization of independently mode-locked lasers is introduced. Its use in synchronizing an octave-spanning Ti:sapphire laser and a 30-fs Cr:forsterite laser yields 300 attoseconds timing jitter measured from 10 mHz to 2.3 MHz. The spectral overlap between the two lasers is large enough to enable direct detection of the difference in the carrier-envelope offset frequency between the two lasers. These are the most important steps in the synthesis of single-cycle optical pulses with spectra spanning 600-1600 nm.     

Generation of attosecond X-ray laser pulses

We propose to generate as-X-ray laser pulses by beating of two or more X-ray laser lines with a frequency separation in the range of 10/sup 15/ Hz. We focus on nickel-like X-ray lasers, some of which have a few almost equidistant laser gain lines with an appropriate difference frequency. It is shown that in the case of three or more lines, these can be phase-locked by means of a Langmuir wave generated in the gain medium at a suitable electron density.     

Passive Laser Beam Combining With Intracavity Interferometric Combiners

In this paper, we present an approach for passive laser beam combining using plane-parallel intracavity interferometric combiners. With this approach, efficient coherent combining of Gaussian laser beams, transverse single high-order-mode laser beams, and even transverse multimode laser beams is possible. We experimentally obtained a combining efficiency of about 90% when coherently combining 16 solid-state laser channels, as well as when coherently combining four fiber laser channels. We also present an arrangement for simultaneous coherent combining and spectral combining, which could possibly overcome current upscaling limits. We present the basic coherent combining approach, review our past and recent investigations and results with both solid-state and fiber laser configurations, and discuss the possible upscaling and future prospects of this approach.     

PC-controlled laser diode system application

This paper presents a system with a personal-computer (PC)-controlled laser-diode beam to make film exposures for generating 256 gray-level images. The hardware equipment of this system includes an IBM PC, an 8255 interface card, and an XY table. Control software is developed to receive image data from commercially available software, such as PAINT SHOP, then convert them to signals for the laser diode and XY table. The gray level of each pixel (picture element) in an image file is represented by an 8-bit binary number. Two ways of control are demonstrated. One way uses this 8-bit number as a parameter for timing delay when the laser diode is on with a constant power output. The other way uses this 8-bit number to go through a D/A converter to control the laser diode for outputting beams with varying intensity. This way may gain higher operation speed, but requires extra hardware. There are two potential applications for this system. One is direct image exposure of yellow, magenta, cyan, and black for all image processing software data outputs, as long as their format is available. The other is for an educational training program to demonstrate the technologies of integrating computer, laser, and color printing     

High-yield external optical feedback resistant partially corrugatedwaveguide laser diodes

This paper clarifies high yield external optical feedback resistant characteristics in partially corrugated waveguide laser diodes (PC-LD's), compared to conventional distributed feedback laser diodes (DFB-LD's). Based on a novel large single dynamic analysis by combining the transient mirror loss (total net threshold gain) fluctuation with the van der Pol equations in single-mode LD's, the feedback effect of mirror loss on the external optical feedback resistance in single-mode LD's was found for the first time. Theoretical analysis predicted that in the PC-LD's, relatively stable transient mirror loss suppresses the positive feedback effect of mirror loss, as well as the optical output fluctuations under the external optical feedback. Experimental results show that the increase of the relative intensity noise in 70% PC-LD's could be suppressed to lower than -120 dB/Hz and the minimum RIN was as low as -126 dB/Hz with the external optical feedback of -20 dB     

Stadium and quasi-stadium laser diodes

We present theoretical and experimental studies on two-dimensional microcavity laser diodes with stadium and quasi-stadium shapes. We report a demonstration of lasing for the first time in a fully chaotic microcavity-a stadium-shaped cavity which is rigorously known to be fully chaotic. We also present systematic studies on quasi-stadium laser diodes for three types of resonator conditions: stable, marginally stable, and unstable. Morphological dependence of lasing characteristics of quasi-stadium laser diodes is elucidated. We also show examples of the application of quasi-stadium laser diodes to beam switching operation and optical signal distribution by using patterned electrodes and the phase locking phenomenon between two resonator modes.     

车轮热轧轮胚尺寸激光测量系统的研究

采用激光测量和视觉测量相结合的方法设计了车轮热轧轮胚尺寸激光测量系统的硬件结构和测量方案,设计了系统的靶标标定方法,并针对高温状态的曲面尺寸进行了测量实验。通过分析实验结果,得到测量系统对于常温状态下车轮轮辋相关尺寸单次测量的标准差分别为0.3865mm、0.1862mm和0.1561mm,20~1000℃热态测量时,测量结果的标准差为0.0390mm。     

纳米级分辨率双频激光回馈位移测量系统

提出了一种基于双频激光回馈原理的高精度位移测量方法。在分析双频激光回馈测量原理的基础上,研究了双频激光回馈的基本现象并给出了理论依据,进一步的在回馈光学系统基础上,对两路正交的光回馈条纹利用电路进行细分处理：即四倍频细分产生大数计数及在一个大数脉冲内再进行小数细分,最后再将二者相结合。主要采用可编程逻辑器件FPGA和单片机设计信号处理电路,四倍频细分主要利用FPGA实现,小数部分主要通过单片机软件查表程序实现。全部电路并通过逻辑、时序仿真,验证了本方法的可行性。目前此系统满足高精度位移测量的要求。     

基于三维激光扫描点云配准的目标位姿测量

地外天体着陆探测是我国深空探测的重要形式和方法,针对地面探测模拟训练系统中探测车位姿提取的需求,提出了一种利用激光扫描仪和标靶球结合的方法进行特征识别,拟合出探测车的位姿数据,并建立地面模拟训练系统。首先对激光扫描数据进行滤波预处理去除点云中离群点,然后选择适当的参数对数据进行重采样。通过基于分类改进的区域增长法对点云进行分割,筛选出指定数量范围的点集并拟合多个标靶球位置信息以建立局部坐标系。通过实验数据分析,标靶球拟合精度满足3mm最大允许误差,点云处理速度得到有效提升,验证了特征识别方法的准确性和高效性。最后通过坐标系转换估计出探测车的位姿矩阵信息。     

CW solid-state ultraviolet laser for optical disk masteringapplication

We have built a prototype laser head that emits 355-nm ultraviolet light in CW mode. The system is based on nonlinear sum-frequency mixing using a β-BaB₂O₄ (BBO) crystal in an external resonator in which two input emissions at 1064 and 532 nm are resonantly enhanced simultaneously. The output exhibits promising characteristics as the master recording laser source, in terms of beam shape and intensity stability. The result of reliability testing of the system in 1000-h real-time operation is also discussed     

原子干涉重力仪集成光源系统综述

高精度重力测量是进行惯性导航、大地测量、空间科学、海洋探测、基础物理研究的重要观测手段,高精度的重力仪一直是科学研究追求的目标。原子干涉重力仪能够提供uGal量级的绝对重力加速度值,是获取高精度重力信息的重要仪器之一,其集成光源系统的设计及实现对其实用化和商业化具有重要意义。首先介绍原子干涉重力仪激光系统的输出需求,然后对国内外典型集成光源系统的相关研究发展进行综述,分别介绍了基于自由空间和光纤传输的两种光源系统的实现方案和发展现状,重点阐述了其稳频、跳频、稳功率等关键技术。最后,对原子干涉重力仪集成光源系统的进行了总结与展望。     

Fundamental characteristics of semiconductor ring laser gyroscopes

Semiconductor ring lasers have many capabilities of realizing new functional devices. In this paper, we propose a novel optical inertial rotation sensor using a semiconductor ring laser. If a semiconductor ring laser operates as an optical inertial rotation sensor, a very small and simple optical gyroscope can be realized. To our knowledge this is the first demonstration of a semiconductor ring laser gyroscope (S‐RLG). Experimental results are as follows. (1) The Sagnac frequency shift can be detected as a beat note by the terminal voltage change of the semiconductor ring laser without branching the circulating optical power. Therefore, the S‐RLG system can be constructed very simply as compared with already proposed optical gyroscopes. (2) The detected beat frequency between two counterpropagating lasers in the S‐RLG is directly proportional to the applied rotation rate. (3) Furthermore, we present data demonstrating the injection locking phenomenon around low rotation rate. These results verify that the proposed S‐RLG operates as an optical inertial rotation sensor based on the Sagnac effect. © 2000 Scripta Technica, Electr Eng Jpn, 132(4): 73–78, 2000     

一种新型双激光测速系统的设计与应用

机动车速度检测是现代智能交通系统中的一个重要组成部分。基于激光测距技术,研究了一种新型双激光机动车测速系统。在沿车流方向的两个固定位置各垂直安装一个激光测距传感器,通过测距值的变化检测到有没有车辆通过,根据车辆通过两个激光测距传感器的时间差和传感器的水平间距,可以计算出车辆的行驶速度。同时测距值可以完整地反映出车辆的外形轮廓。该系统主要由事件检测模块、数据协议转换模块以及轮廓检测器模块组成。通过与美国STALKER公司的BASIC型移动式测速仪测试数据进行比对实验,结果表明该系统测量误差在1 km/h之内,具有成本低、测速快和精度高的特点。     

Improved parallelism measurement using a laser interferometer

The authors discuss an improved method for obtaining parallelism measurements of two straight bars in a plane, considering the specific problem of making two vertical surfaces parallel to each other to within 0.00005 of an inch over a 50 inch length. The authors compare the existing method of using dial indicators and a slider with that of using a laser interferometer, cable and pulley system, and a microcomputer. Possible errors this system may generate and solutions to help minimize them are presented. The procedure presented will help to minimize errors due to the operator such as `reading between the lines' on an indicator and hand applied pressure. These methods allow improved parallelism resolution over that obtainable with the indicator     

Coherent Beam Combining of Fiber Amplifiers Using Stochastic Parallel Gradient Descent Algorithm and Its Application

We present theoretical and experimental research on coherent beam combining of fiber amplifiers using stochastic parallel gradient descent (SPGD) algorithm. The feasibility of coherent beam combining using SPGD algorithm is detailed analytically. Numerical simulation is accomplished to explore the scaling potential to higher number of laser beams. Experimental investigation on coherent beam combining of two and three W-level fiber amplifiers is demonstrated. Several application fields, i.e., atmosphere distortion compensating, beam steering, and beam shaping based on coherent beam combining using SPGD algorithm are proposed.     

Surface microstructuring of aluminum alloy 2024 using femtosecondexcimer laser irradiation

Surface microstructuring and modification of aluminum alloy 2024-T3 were investigated using a femtosecond pulse laser irradiation. The surface micrographs of the scanning electron microscopy were characterized as a function of incident laser fluence. The surface features ranging from submicrometer to micrometers were developed through the variation in laser fluence and laser pulse count. Results indicated that surface patterns were uniquely constructed in a controlled use of pulsed laser parameters for the ablation. Two ablation regimes were found in the logarithmic dependence of the ablated depth on laser fluence and two components were attributed to the optical and energy penetration. A thermal dynamic model was adopted to analyze the ablation processes, and the theoretical analysis agreed well with the experimental results     

Petawatt laser system and experiments

We have developed a hybrid Ti:sapphire-Nd:glass laser system that produces more than 1.5 PW of peak power. The system has produced up to 680 J of energy on target at 1054 nm in a compressed 440/spl plusmn/20-fs pulse by use of 94-cm diffraction gratings. A focused irradiance of up to 6/spl times/10/sup 20/ W/cm/sup 2/ was achieved using an on-axis parabolic mirror and adaptive optic wavefront control. Experiments with the petawatt laser system focused the beam on solid targets and produced a strongly relativistic interaction. Energy content, spectra, and angular pattern of the photon, electron, and ion radiations were diagnosed in a number of ways, including several nuclear activation techniques. Approximately 40-50% of the laser energy was converted to broadly beamed hot electrons, with an associated bremsstrahlung beam. High luminosity ion beams were observed normal to the rear surface of various targets with energies up to /spl ges/55 MeV, representing /spl sim/7% of the laser energy. These and other results are presented.