荧光偏振短距激光雷达测量生物战剂/气溶胶

Bio-agents and aerosol measurement by fluorescence and depolarization short-distance lidar

基于激光诱导荧光(LIF)原理和弹性散射作用于非球形粒子上产生的偏振特性,设计研制了短距测量荧光和偏振激光雷达:采用了三个激光光源、两个接收望远镜、一个退偏组件和一个荧光光谱特征分析光谱仪,设计遥测探测距离为200 m至数千米。荧光测量采用了Nd:YAG激光器的三倍频355 nm和4倍频266 nm输出,激光束脉冲宽度约为6 ns,重复频率为20 Hz,荧光接收光学及光谱分析子系统由25.0 mm口径的f/4牛顿望远镜,车尔尼特纳光谱仪和32通道的光电倍增管(PMT)等组件组成;偏振和弹性散射信号由孔径12.5 mm的卡塞格林望远镜接收。荧光测量的信噪比仿真计算表明:以最小SNR=10作为参照,在1 km距离上,白天探测不到数浓度为10 000个/升的战剂云团,但在夜间则可以获得较好的信号强度;偏振测量结果初步分析表明:(1)退偏比表现出较强的波长依赖性;(2)多波长退偏比测量可以显著提高生物战剂的鉴别能力。

Based on two independent physical phenomena： laser induced fluorescence（LIF） and depolarization resulting from elastic scattering on non-spherical particles, a short range lidar system for real-time standoff detection of bio-agents was developed. The lidar system included three laser sources, two receiving telescopes, one depolarization component and fluorescence spectral signature analyzing spectrograph. It was designed to provide the stand-off detection capability at ranges from 200 m up to several kilometers. For fluorescence excitation, 3rd （355 nm） and 4th （266 nm） harmonics of Nd：YAG pulsed lasers were used. They emitted short （about 6 ns） pulses with the repetition frequency of 20 Hz. Collecting optical system for fluorescence echo detection and spectral content analysis included 25.0 mm diameter f/4 Newton telescope, Czerny Turner spectrograph and a 32-channel PMT. The depolarization and Mie echo signal were collected by a Cassegrain telescope with an aperture diameter of 12.5 mm. Through the simulative calculation of SNR of fluorescence measurement, it was found that, with the minimum detectable SNR value of 10 as reference, the bio-agent cloud with concentration of 10 000ACPLA at the distance of 1 km could not be detected in daytime, while a rather good signal intensity could be obtained in nighttime. The preliminary analysis to the depolarization measurement results indicated that： （1） the depolarization ratios were wavelength-dependent; （2） depolarization measurement using multiple wavelengths could increase discrimination efficiency significantly.