机载激光诱导荧光遥感系统相关参数的讨论

以文献[1]所设计的机载激光诱导荧光遥感成像系统为例,简要地分析了该遥感系统的荧光参数、信噪比、飞机飞行参数与系统性能的关系。探测器接收到的荧光强度和信噪比除了与激光器发射的功率、被激发物质的荧光量子效率、密度、浓度和探测器的量子效率等成正比外,还受遥感系统的仪器结构、探测器的灵敏度、荧光寿命、阳光的反射,以及大气散射等因素的影响。给出了遥感系统的空间分辨率与飞机飞行高度和速度、激光扫描频率和脉冲发射频率之间的关系。分析结果对实际研制机载激光荧光遥感系统有重要的参考价值。     

Self-mixing interference in an all-fiberized configuration Er-Yb codoped distributed Bragg reflector laser for vibration measurement

Self-mixing sensing technique can be used for measuring distances, displacements, velocities and vibration. In this paper, for good sensitivity vibration measurement system, self-mixing vibrator using an all-fiberized configuration Er³⁺-Yb³⁺ Distributed Bragg Reflector (EYDBR) laser is proposed and investigated for the first time. Results obtained demonstrate that all-fiberized configuration EYDBR laser present a powerful tool for the advancement of self-mixing vibration sensor and provide a potential remote measurement of the vibration compared with the optical feedback in other traditional fiber lasers.     

Threshold characteristics analysis of one-end-pumped Yb3+-doped gain-guided and index-antiguided fiber laser

An exact analytical expression of the threshold pump power for the one-end-pumped Yb³⁺-doped gain-guided and index-antiguided (GG–IAG) fiber laser has been obtained by solving the improved rate equations (REs) with the additional leakage losses. The effects of Yb³⁺ concentration, fiber length, core radius and mirror reflectivity on the threshold pump power are discussed. After optimizing, the results show that the laser threshold of GG–IAG fiber laser can be greatly reduced while maintaining single mode oscillation. Compared to the numerical methods, the analytical expression has easy calculation and distinct results.     

A photon pressure calibrator for the GEO 600 gravitational wave detector

Interferometer mirror displacement induced by radiation pressure is used to demonstrate an alternative calibration method for the GEO 600 detector. The photon calibrator utilizes an amplitude modulated laser diode with up to 1.4 W output power at a wavelength of 1035 nm. The achieved accuracy of the strain amplitude calibration is dominated by the laser power calibration error, which is in the range of ±4% for the measurements presented in this Letter.     

硅陷阱探测器在350—1064 nm波段的绝对光谱响应度定标

介绍了利用钛宝石可调谐激光器、倍频器和单波长激光器作为光源,在24个波长分立点定标了三个硅陷阱探测器的绝对光谱响应度,解决了红外激光的精确定位与调整、窗口透过率模拟定标等关键技术.结果显示：在激光波长为412—800nm时,三个陷阱探测器定标的不确定度约低于0.05％;当激光波长大于800nm以及低于355nm时,获得的陷阱探测器的定标不确定度约低于0.065％.硅陷阱探测器可以作为空间各类遥感器在350—1064nm波段定标的传递标准探测器. 关键词： 陷阱探测器 低温辐射计 光谱响应度 辐射定标     

Low-energy ion emission from a xenon gas-puff laser-plasma X-ray source

We have measured low-energy ion emission from a gas-puff laser-plasma X-ray source. The ions may cause the degradation of the condenser mirror of the extreme ultra-violet projection lithography system. A 0.7 J in 8 ns Nd:YAG laser at 1.06 μm was focused onto the xenon gas-puff target with an intensity of ∼10¹² W/cm². The silicon (111) plates, placed at a distance of 32 mm from the laser-interaction region, were exposed with the xenon ions. The average ion energy was measured to be less than 50 eV with a Faraday-cup detector placed close to the silicon plates. The xenon deposition occurred in the silicon plates with a depth of less than 40 nm. The deposition density was measured with a quadrupole secondary ion mass spectrometer to be 10²¹ /cm³ after 1500 laser shots. The energy-conversion efficiency from the laser energy into the ions is ∼0.1%/4 π sr/shot. For the lithography system, if we can remove such ion bombardment completely using novel techniques such as electro-magnetic devices or gas flow curtain techniques, the lifetime of the condenser mirror will be extended significantly. Received: 20 November 2000 / Published online: 9 February 2001     

自动聚焦激光诱导击穿光谱远程测量系统

激光诱导击穿光谱(LIBS)技术具有非接触测量、无需样品预处理以及快速多元素同时分析等特点,适合于高温、高压、真空、有毒以及敌对环境等仪器和操作人员无法靠近观测对象的应用中。LIBS技术结合望远镜系统可以实现物质成分的远距离检测与分析。搭建了一套可自动聚焦的LIBS远程测量系统。该系统中的望远镜采用Schwarzschild结构,由一块凹球面反射镜和一块凸球面反射镜组成。两块球面反射镜共轴安装。其中凸面反射镜安装在电控精密平移台上,电动平移台可带动凸面反射镜沿光轴移动。通过调整凸面反射镜的位置,改变凸面反射镜和凹面反射镜的间距,进而改变系统的焦距,实现对不同距离的样品进行光谱测量。该结构的优点在于：激光聚焦光路与信号光采集光路相同,便于安装和调试;望远镜系统采用全反射式光路,适用于紫外波段检测;只包括两个球面反射镜,结构紧凑,元件容易加工。望远镜系统调焦距离为1.5～3.6 m,聚焦光斑直径约为0.5~1.0 mm。使用该系统对铜样品进行了LIBS实验,确认了Cu元素的特征谱线。通过测量Cu元素的LIBS特征谱线(Cu Ⅰ 223.01 nm, Cu Ⅰ 224.43 nm)峰面积和反射镜间距之间关系,得到了激光的最优聚焦位置。实验结果表明,该系统能够完成样品的远程激发和LIBS光谱测量,并能够对不同距离的样品进行自动聚焦。     

激光诱导荧光遥感系统的设计

分别设计了地面车载 (或海面 )和空中机载激光诱导荧光雷达成像遥感系统。提出了用拼合式卡塞格仑(Cassegrainnian)望远镜结构实现多色荧光成像系统。所设计的系统可以同时获取荧光光谱信息、荧光信息成像和与荧光信息相匹配的地理信息。所设计的系统与以住的激光荧光遥感系统相比 ,增加了荧光成像功能。机载设计方案是一个适应RS、GPS、GIS一体化和“数字地球”发展要求的激光遥感空间信息集成的设计 ,具有一定的先进性。     

Optimization of passively <Emphasis Type="BoldItalic">Q</Emphasis> -switched Er:Yb:Cr:phosphate glass laser: theoretical analysis and experimental results

This article presents the results of theoretical analysis and experimental studies on passively Q-switched flash-lamp pumped Er: Glass laser employing Co²⁺:MgAl₂O₄ saturable absorber. Using two methodologies derived from basic rate equations, laser performance was optimized in terms of the output energy, pulse width and efficiency. The efficacy of these approaches is compared with each other and these results matched well when evaluated for a given system. Theoretical results have been compared with the actual experimental results. For optimum combination of output mirror reflectivity (R=70%) and initial transmission of saturable absorber (T₀=83%), single pulse energy of 10.77 mJ, 35.6 ns pulse width was obtained with a Q-switching efficiency of 12.7%. The experimental results match well with the theoretical analysis. To the best of our knowledge, this is the first attempt to analyse passively Q-switched Er:Glass laser by Co²⁺:MgAl₂O₄ from both these approaches. PACS 42.60.Gd, 42.55.Rz     

Generation of powerful filaments at a long distance using adaptive optics

Because of its extraordinary properties (intensity clamping, white light source, km long plasma channels), filamentation represents an ideal candidate for remote sensing. However, the promising generation of filaments at long distances for such purposes remains an issue.

We propose a specially designed focusing telescope to properly deliver the laser pulses at long distance and generate powerful filaments. The telescope includes a deformable mirror (DM) that corrects the wavefront’s aberrations working in a closed loop system with a wavefront sensor (WFS). Using this setup we are able to generate extraordinarily strong nitrogen signals at a distance as far as 90 m using 40 mJ laser pulses. Compared to the chirped based filament control technique, we believe that an appropriate control of the reservoir like what we have achieved will contribute to reduce the energy of the required laser pulses and at the same time, the cost of the required laser system.     

用于大气遥感的远紫外光栅色散成像光谱仪的研究

远紫外光栅色散型成像光谱仪在空间大气遥感领域主要用于电离层、热层、极光和辉光的探测。文章根据临边与天底结合的大气成像光谱探测原理,提出了探测方案,设计了适用于远紫外波段的光栅色散型成像光谱仪的两种光学系统,并选择了平面光栅结构进行研制集成,在国内首次获得了原理样机。样机工作波段为120～180nm,望远系统采用离轴抛物镜,光谱成像系统采用改进型的Czerny-Turner结构,探测器使用远紫外响应背照型增强CCD。搭建了相应的实验系统对样机的基本性能参数进行了测试,测得光谱分辨率约为2nm,空间分辨率0.5mrad。这种远紫外光栅色散型成像光谱仪的研究对完善我国大气遥感事业具有重要的研究与应用价值。     

Adaptive aberration correction based on ant colony algorithm for solid-state lasers: numerical simulations

We describe an adaptive aberration correction technique based on an ant colony algorithm for solid-state lasers and a general class of other adaptive optics systems. We show that it is possible to compensate phase aberrations without wavefront sensing in this approach, which iteratively adjusts the control voltages of a deformable mirror to maximize certain system performance metrics of the far-field intensity distribution of the laser beam. The effectiveness of this approach is analyzed numerically by use of a 37-element piezoelectric deformable mirror and a variation of the Strehl ratio as the metric. Results demonstrate that this approach can effectively compensate the phase distortions of laser beams and significantly improve beam quality. A comparison indicates that this approach is much faster than a genetic algorithm while achieving almost the same beam quality.     

Laser backscattering analytical model of Doppler power spectra about rotating convex quadric bodies of revolution

We propose an analytical model of Doppler power spectra in backscatter from arbitrary rough convex quadric bodies of revolution (whose lateral surface is a quadric) rotating around axes. In the global Cartesian coordinate system, the analytical model deduced is suitable for general convex quadric body of revolution. Based on this analytical model, the Doppler power spectra of cones, cylinders, paraboloids of revolution, and sphere–cones combination are proposed. We analyze numerically the influence of geometric parameters, aspect angle, wavelength and reflectance of rough surface of the objects on the broadened spectra because of the Doppler effect. This analytical solution may contribute to laser Doppler velocimetry, and remote sensing of ballistic missile that spin.     

高分辨率星载真空紫外成像光谱仪设计与研究

为了实现对大气层中辐射波长分布在真空紫外和近紫外波段(115～300 nm)的粒子探测,完善大气遥感,设计了一种高分辨率成像光谱仪,并开展了原理样机的研制.根据国外已有载荷进行分析,选用了以离轴抛物镜为望远系统、Czerny-Tumer结构为成像光谱系统的光学方案;针对真空紫外波段辐射弱的特点选取了带有MCP的二维光子...     

Double passage analysis in random media using two-scale random propagators

Abstract

In location and remote sensing experiments there arise a number of effects related to the double passage of the backscattered field through the same random inhomogeneities as the incident one. To account for the correlation of the forward–backward propagating events, there is a need for a measure in which the random information along the propagation path is preserved. For the generation of even statistical moments, the relevant measure defined in the recently formulated stochastic geometrical theory of diflraction is the two-point random function (TPRF)—a paired field measure which is propagated along the geometrical rays of the deterministic background medium. From this function all even statistical moments can be generated. Here we present an approximate analytical solution for the high-frequency propagator obtained by applying the multiscale expansion asymptotic procedure to the partial differential equation governing the propagation a1 the TPRF. The test of the solution is performed on canonical backscattering problems based on point source–point scatterer and paint source–plane mirror configurations, which justifies its further application for construction of the coherence measures of the rctrareflected field. Coherence properties of the plane and spherical wavefields reflected backward by a plane mirror were investigated. Further, we investigated the intensity enhancement effects observed in the double passage of a Gaussian beam retroreflected from a plane mirror. Asymptotic expressions lor the retroreflected intensity are obtained, and their computations show good agreement with the direct numerical evaluations.     

基于可调谐二极管激光吸收光谱遥测CH4浓度

文章对可调谐二极管激光的直接吸收和波长调制光谱进行了理论分析,设计了一套用于研究甲烷吸收特性的测量系统.近红外二极管激光工作在室温下,选用波长为1.65 μm,利用甲烷的2v3带R(3)线实现对甲烷气体的吸收测量,对测量的信噪比和系统的基本噪声源进行了分析,为实现甲烷浓度的在线遥测打下基础.     

Intensity vibration sensor based on Raman fiber laser using a distributed mirror combined with Bragg grating structures

In this work, the authors propose a new configuration for an intensity vibration sensor based on a Raman fiber laser. The linear cavity of the Raman fiber laser relies on the combination of a distributed Rayleigh mirror and fiber Bragg gratings, which are used as the sensing element and intensity filter. The sensor was able to measure vibrations with frequencies of up to 350 Hz with more than 50 dB of signal-to-noise ratio (SNR) and also the amplitude of the vibrations with a sensitivity of up to 0.57 ± 0.07 dB/με for vibrations with a maximum strain variation of up to 35 με. The main advantages of the proposed configuration are the simple scheme with high SNR for remote sensing and the easy possibility of multiplexing.     

Analysis and modelling of high power laser beam position sensing

A new theory using a rotating convex mirror to reflect part of a laser beam into a pyro-electric sensor in order to detect the high power laser beam position is addressed in this research. The experiments were performed on the Nd: YAG laser system. The sensing performance was tested with the average power up to 50 W, duration time 1 ms and duration frequency 360 Hz. The results of static experiments show that the sensing system designed and developed in this research may correctly detect the Nd: YAG laser beam with the system parameters varied. The results of dynamic experiments show that the average sensing accuracy of beam position is up to 90% with a wide variation of laser system parameters.     

Dispersionless saturable absorber mirrors with large modulation depths and low saturation fluences

We show that it is possible to eliminate group delay dispersion over wide bandwidths in low-finesse, resonant saturable absorber mirrors, whilst maintaining a low saturation fluence and a high modulation depth. By modelling the mirror structure we demonstrate that these properties can be produced by capping a resonant device with a single dielectric layer of carefully selected refractive index. We show that a specially capped dispersionless structure minimises the temporal broadening of femtosecond pulses reflected from the mirror. We compare this device against uncapped-resonant and anti-resonant structures. The superior performance of the capped, dispersionless device was verified experimentally by comparing resonant, anti-resonant and dispersionless quantum-dot (QD) saturable absorber mirrors incorporated into a Cr⁴⁺:forsterite laser system. We found that a minimum pulse duration of 86 fs could be achieved for the dispersionless structure at 1290 nm with an output power of 55 mW compared to 122 fs in an anti-resonant structure and several-picosecond pulses for a resonant structure.     

旋转镜鼓式热像仪的光雷达回波特性

 旋转镜鼓式热像仪对光场的扫描主要由镜鼓来完成，在激光束的照射下，镜鼓棱及其邻域的后向散射不可避免地给散射光引进了一个附加的多普勒频移。对平行光束经热像仪后的动态回波特性进行分析研究，提出了一种测量光束多普勒频移的方法，并建立了相应的实验系统。实验结果与理论分析是一致的，为判别热像仪的工作方式提供了一种可能的方法。