亚稳态氦激光雷达的研制进展

Progress on developing metastable helium Lidar

亚稳态氦激光雷达通过发射调谐至亚稳态氦原子的1083.0 nm共振线的激光来探测热层和外逸层的亚稳态氦原子数密度。能够覆盖的探测范围约为200~1000 km。在这个高度范围内,亚稳态原子密度较小,随着季节的变化,数密度最大通常不超过1 cm-3。中国科学技术大学目前正在研制基于六个1 m口径望远镜阵列和高能量1083 nm脉冲激光器的亚稳态氦共振荧光激光雷达。雷达的望远镜有效面积约4.8 m2;1083 nm脉冲激光器采用光参量震荡(OPO)和光参量放大(OPA)技术,以532 nm高能量脉冲作为泵浦光,最终输出单模窄带宽(300 MHz)的1083 nm脉冲光;接收端采用深度制冷(-120℃)的InGaAs探测器,量子效率大于30%,暗计数可控制在100 s-1以内;滤波模块采用干涉滤光片和FPI超窄带滤波串联的方式,最终将滤波半宽压缩到10 GHz左右,峰值透过率55%。综合以上关键技术指标,在数密度较大的季节,信噪比可能达到约400,在数密度较小的季节,信噪比约为10。

Metastable helium Lidar detects the metastable helium density in the thermosphere and exosphere by emitting 1083.0 nm laser,which is locked at the resonance lines of metastable helium atoms.The detecting range can cover the altitude from 200 km to 1000 km.In this height range,metastable helium density was quite low,usually lower than 1 cm-3.University of Science and Technology of China(USTC)was now developing metastable helium resonance fluorescence lidar based on six 1 m-diameter telescopes array and high power 1083 nm pulse laser.The effective area of this telescope array was 4.8 m2;The high power pulsed 1083 nm laser employed optical parametric oscillation(OPO)and optical parametric amplification(OPA)techniques,used 532 nm pulses as pumping laser,and emited single mode 1083 nm pulses with a frequency bandwidth of 300 MHz;The receiving system employed a InGaAs single-photon-counting detector with deep cooling(-120℃),the quantum efficiency was higher than 30%accompanied with a dark count lower than 100 s-1;The background noise was filtered by series-connecting of interference filter and FPI ultra-narrow-band filter.The final filtering bandwidth was 10 GHz and the peak transmittance was 55%.Based on the above key performance of the system,the SNR would be about 400 in the strong-signal season and 10 in the weak-signal season.