短波辐射源测向定位的一些特殊性

波长为200m～10m（相应的频率为1．5MHz～30MHz）的电波通常被称为短波。短波既可由地波传播，也可由天波传播。地波（地表波）是沿地球表而传播的无线电波，天波是经电离层反射回地面的无线电波。     

Passive harmonic mode-locking in all-fibre soliton laser: energystates and stability aspects

The behaviour of a passively mode-locked soliton laser, under different energy states, is studied by using a numerical simulation. The shorter pulse obtainable is determined, pointing out the soliton properties of the output pulses. In the case of harmonic mode-locking, power quantisation related to the number of existing pulses in the cavity, is obtained and repetition rate instability is detected. It is found that by introducing a narrow band optical filter in the cavity and by optimising the filter bandwidth, this instability is substantially reduced     

谐波过程的高阶广义各态历经性的分析与应用

高阶统计在信号处理的许多领域得到了广泛应用。但在实际应用的许多情况下,由于只能得到观测过程的一个样本,所以只能用样本的时间平均来代替其统计平均。其前提是过程对该统计量具有广义的各态历经性,该文分析了谐波过程高阶统计量的各态历经性,得到了谐波过程满足三阶、四阶矩和累积量广义各态历经的充要条件。然后研究了这些条件在高阶统计量的相位耦合识别、高阶阵列处理方法等问题中的应用,并进行了模拟实验验证。     

Marginal stability design criterion for gyro-TWTs and comparison of fundamental with second harmonic operation

Stability properties of both the fundamental and second harmonic gyrotron travelling wave amplifier (gyro-TWT) are examined with multi-mode particle simulations. The second harmonic cyclotron interaction with an axis-encircling electron beam is found to be more stable to oscillations and can yield significantly greater power than the fundamental harmonic gyro-TWT. A multiple stage interaction structure based on a marginal stability criterion is proposed and illustrated with examples of a 128kW fundamental gyro-TWT and a 532 kW second harmonic gyro-TWT, Stable amplification at much higher power levels is in principle possible.     

基于主动锁模控制的激光谐波研究

介绍一种采用主动锁模控制产生超短激光脉冲序列的方法。首先通过基于主动锁模激光系统的参量自治微分方程思想,导出了系统出现稳定条件时参数设置方法。然后利用铌酸锂的非线性,展开成贝赛尔系数的函数级数,载频与边频数差为调制频率的整数倍,最后产生高重复频率超短光脉冲,得到高阶锁模脉冲,实验结果表明:其通过调节调制器的调制参数来控制谐振腔中的模式损耗,在调制频率为１ＧＨz量级的情况下,可获得重复频率１０ＧＨz的超短光脉冲序列,有啁啾时脉冲时域形状是很好的高斯型,没有出现明显畸变。     

The generation and frequency measurement of short-wavelength far-infrared laser emissions

A significantly improved three-laser heterodyne system has been assembled to generate and measure short-wavelength far-infrared (FIR) laser emissions. Over the past several years, this system has been used to discover fifty-five FIR laser emissions, ranging in wavelength from 26.3 to 185.0 /spl mu/m. These emissions were generated by optically pumping a FIR cavity with a continuous-wave carbon dioxide laser in a X-V geometry when using either hydrazine or a methanol isotopologue as the FIR laser medium. Although heterodyne techniques can be used to measure the frequencies of these FIR laser emissions with fractional uncertainties of /spl plusmn/2/spl times/10/sup -7/, shortcomings in the previous system limited its effectiveness. Improvements made to the three-laser heterodyne system have resulted in an increase in the spectral range used to search for the beat between the known and unknown laser frequencies (an increase of up to 25 GHz) as well as an increase in the system's sensitivity (by up to a factor of 30), all without requiring the use of an additional microwave frequency source. With this improved system, the FIR laser frequencies for the recently discovered 53.9- and 90.0-/spl mu/m laser emissions generated by optically pumped CH/sub 3/OD have been measured.     

Small particle detection method based on laser feedback

In order to overcome the shortcomings of traditional particle measurement, a new method for the detection of small and single particles through laser feedback phenomenon is presented. This method is based on the laser feedback caused by radiation scattered back from a moving particle in the external cavity of the laser. The parameters of the single particle, such as the diameter, velocity, and quantity, can be measured and calculated from the change in output laser power. In the experiment, the confocal external cavity composed of a concave reflector and a positive lens is designed. This device is able to obtain the corresponding variety curve of standard particles passing through the confocal area, and then the parameters of the particles can be measured and calculated by combining the experimental data and standard curves. Experimental results show that this method is an easily operated and reliable way for particle detection. The measurement ranges from 0.2 to 2000 μm, resolution is 0.2 μm, and measurement error is within 2%. This device may have wide application in areas such as atmosphere particle detection and calibration of a single particle producer.     

基于粒子受激散时的烟雾粒子的检测与识别

本文提出了一种基于粒子激光散射来检测和识别非火灾烟雾的吸气式多传感器阵列烟雾探测系统,详细阐述了该系统的结构和信号处理方法;同时提出了利用计算机求解不同物质粒子Mie散射系数的实际计算公式并推导出典型物质粒子的散射光强分布。     

Free electron laser based on the Smith-Purcell radiation

The electromagnetic radiation is sti mulated when anelectron beampasses a metallic periodic structure like adiffraction grating at a fixed distance close to the sur-face.This phenomenon is known as the Smith-Purcelleffect .The radiation mechanism was pred…     

强激光作用下等离子体尾波引起奇次谐波辐射的理论分析

对库仑规范的激光与等离子体相互作用的耦合方程进行了准静态处理,同时利用处理后的方程从理论上完整规范地求出了相互作用的非线性辐射谐波分量。讨论分析了其谐波成分中只有奇次分量的原因和影响因素。通过给定参数的计算,作出了辐射谐波的能谱图,并发现相邻谐波辐射相差几百倍。     

基于激光散射理论的微小颗粒测量的数值分析

根据算法的准确性、稳定性和快速性原则, 讨论了Mie散射和Rayleigh散射的数值算法。将Mie散射理论及Rayleigh散射理论的Matlab数值结果与Wiscombe结果对比分析, 证明了此Matlab程序的正确性。在此基础上, 确定了当颗粒粒径参量x0.3时采用Rayleigh散射理论来确定前向某一角度范围内散射光能分布, 从中求得颗粒的粒径大小和分布, 具有比Mie散射理论算法快速性的特点。该方法为某些测试对象(颗粒与分散介质相对折射率、颗粒种类等)确定、微小颗粒的在线测量提供了理论支持。     

Efficient second harmonic conversion of broad-band high-peak-powerNd:glass laser radiation using large-aperture KDP crystals in quadrature

The authors have investigated the second-harmonic conversion efficiency of broadband Nd:glass laser light (Δν/c<30 cm^-1 FWHM). Using two KDP crystals in a quadrature arrangement, they obtain energy conversion efficiencies of ≈55% with an initial bandwidth for the fundamental of Δν/c≈17 cm^-1 FWHM. For these conditions, a modest increase (≈70%) was observed in the harmonic bandwidth (FWHM) relative to the fundamental. The usual theory of three-wave mixing in dispersive birefringent nonlinear crystals is extended to describe the broadband harmonic conversion process; the generalized theory includes the statistical properties of the light and phase mismatch effects on the spectral components in the complex field amplitudes. Good agreement is found between the code calculations and the measurements     

基于SOA非线性偏振旋转效应谐波锁模光纤激光器的数值研究

基于半导体光放大器(SOA)的锁模光纤环行激光器因其能得到高质量、高重复率的光脉冲而受到人们的广泛关注.在考虑SOA非线性偏振旋转效应下,建立了基于SOA的谐波锁模光纤激光器理论模型,利用该模型,着重研究了在不同SOA注入电流情况下,SOA非线性偏振旋转效应对谐波锁模光纤激光器输出脉冲波形、峰值功率及脉冲宽度的影响.研究结果表明:当SOA注入电流分别为102 mA和106 mA时,可以获得峰值功率为0.16 mW和0.56 mW、脉冲宽度为6 ps和19.8 ps的稳定锁模脉冲.     

Active antenna for improved efficiency and reduced harmonic radiation

Harmonic suppressed active antenna integrated with power amplifier yields improved efficiency, higher output power and reduced harmonic radiation from transmitter front end. This paper presents different harmonic suppression techniques of active antenna integrated with power amplifier. This paper also proposes and demonstrates novel PBG engineered structures to suppress higher order harmonics of integrated active antenna.     

粒子滤波的机载激光通信自适应参数辨识跟踪方法

机载空间激光通信是实现未来超大容量空间通信的主要途径,机载空间激光通信终端的高精度实时动态跟踪一直是其研究的难点问题。为了解决机载空间激光通信终端的机动形式多样性的问题,提出了自适应参数辨识粒子滤波方法。在连续的时间域中,基于三阶线性微分方程的参数辨识模型描述机载空间激光通信终端运动,该模型能适应机载激光通信终端的多种运动模式,粒子滤波能处理非线性/线性高斯问题,因此可以引入到参数辨识模型中。实验结果表明:该算法能改善收敛精度,对工程应用也有重要意义。     

基于粒子群算法的激光位移传感器参量优化

为了提高激光三角测距精度、优化传感器设计过程中的光学参量,采用数学建模和计算机辅助分析的方法,解析了激光三角测距传感器中的关键参量与测量系统各指标的关系,并采用一种基于粒子群算法的参量优化方法,得到符合系统优化要求的光学参量,进行了理论分析和验证。结果表明,在进行参量设计时,各参量相互牵制;确定了粒子群搜索空间和约束;在灵敏度S_min达到2.2386mm时,系统分辨力可达到2.8μm,且其它各参量取值符合系统要求,同时优化效率大大提高。该优化方法算法简单、操作方便。     

Intermodulation and harmonic distortions of laser diodes withoptical feedback

Analytical expressions for the second-order harmonic and the third-order intermodulation distortions of laser diodes with optical feedback are derived. It is shown theoretically and experimentally that optical feedback from the transmission fiber considerably enhances intermodulation and harmonic distortions of laser diodes. Third-order intermodulation distortions up to -15 dBc must be expected for two-tone modulation and low-intensity modulation indexes m≈7% per carrier, which affects the performance of subcarrier multiplexed (SCM) communication systems. To avoid additional distortions the external feedback level must be two orders of magnitudes lower than the critical external feedback level of the laser diode     

基于激光谐波调制的深孔内壁三维面型分析系统

为了快速精确地获取深孔结构内壁三维面型,从而分析深孔加工质量,提出了一种基于激光谐波调制的线型扫描系统,设计了可深入深孔结构的反射式光学系统。研究了通过时间窗滤波的谐波匹配点云优化算法,该算法利用谐波调制相位范围对近轴线扫描区域进行阈值分离,从而完成点云数据的滤波。实验针对三种不同类型的深孔进行了测试,并采用Handyscan三维成像仪进行了点云数据对比。文中对5 cm×5 cm的内壁区域进行了量化分析, 对比了优化前后的三维点云图像。优化前的点云中明显包含很多杂散点,综合平均偏差为0.53 mm,而采用优化后,噪声被有效抑制,综合平均偏差降为0.12 mm。在x轴方向上,系统位置偏差均值为0.240 mm,在y轴方向上,系统位置偏差均值为0.228 mm。由于优化后降低了需要计算的点云总量,故其收敛速度也有一定的改善,在3000点以上趋于稳定,约为优化前用时的65.8%。可见该系统适用于深孔内壁三维面型检测,为深孔测试与数据降噪提供了新的思路。     

Tensile strained QW structure for low-threshold operation of short-wavelength, AlGaInP LDs emitting in the 630 nm band

The amount of tensile strain introduced into QWs and the optimum QW structure are evaluated for low-threshold operation of AlGaInP LDs in the wavelength range 630-640 nm. Very low threshold current of 32 mA under CW operation at 20 degrees C is achieved in an index-guided SQW LD emitting at 632 nm.<>     

Multipulse operation and limits of the Kerr-lens mode-locking stability

Numerical analysis in combination with experimental data for Cr/sup 2+/:ZnSe and Ti:sapphire lasers reveal the following main mechanisms of multiple-pulse generation for Kerr-lens mode-locked solid-state lasers: 1) continuum amplification due to a spectral loss growth for ultrashort or chirped pulses and 2) a bounded perturbation rise for high-energy pulses. The role of such laser parameters as gain saturation and relaxation, saturable and unsaturable loss, self-phase modulation, Kerr-lensing, and pump intensity is analyzed. This analysis provides basic directions for single-pulse stability enhancement and for multiple-pulse generation control.