物理学报2018，Vol.67Issue(1)：120-129,10.DOI:10.7498/aps.67.20171025
基于波长330 nm激光激发多色激光导星回波光子数的数值计算与探讨
Numerical calculation and discussion on return photons of polychromatic laser guide stars by a laser beam with 330 nm wavelength
摘要
Abstract
The properties of return photons of polychromatic laser guide stars excited by a modeless laser with 330 nm wavelength are investigated in this paper by numerical simulation. The repetition rate, linewidth, initial diameter of laser spot and atmospheric transmittance have great influences on the return photons at 330 nm and 2207 nm from polychromatic laser guide stars. First, the laser linewidth is optimized by solving the rate equations of interaction between laser and sodium atoms. We find that the 0.6 GHz linewidth for the continuous wave laser and the 1.0 GHz linewidth for the pulse laser are beneficial to obtaining the higher excited probability of sodium atoms. Based on the fitted relation between the excitation probability of sodium atoms and laser intensity, considering the random distributions of laser intensity at the mesosphere due to the influence of atmospheric turbulence, the return photons from polychromatic laser guide stars are numerically calculated. The results show that the return photons at 330 nm excited by the continuous-wave laser are more than those excited by the pulse laser. And the return photons excited by continuous-wave laser almost do not fluctuate when laser power arriving at sodium layer is 1 W. Furthermore, effects of the repetition rate of pulse laser and the laser initial diameter on the return photons at 330 nm are studied. The two results are obtained as follows. The first result is that the increment of return photons at 330 nm will converge to a constant value when the repetition rate of pulse laser is over 50 kHz. The second result is that the initial diameter of continuous wave laser has no effect on the return photons but the effect of pulse laser is more obvious. Particularly, the atmospheric transmittance is an important factor of influence because it causes a severe loss of light power at 330 nm wavelength. Under the conditions of 5 km atmospheric visibility and 12.8 cm atmospheric turbulence coherence length, the launched power of pulse laser with 50 ns duration should be more than 34 W for obtaining enough return photons required for the effective detection of atmospheric turbulence tip-tilt with the natural stars. But for the continuous-wave laser, the launched power should be more than 20 W. In the case of 10 km atmospheric visibility, if the same return photons at 330 nm are required, the launched power of pulse laser will also be more than that of the continuous-wave laser under the same conditions. Therefore, the continuous-wave laser has more advantages than the pulse laser in exciting the polychromatic laser guide stars. We hope that the above results will be beneficial to the further experimental research.关键词
多色激光导星/连续激光/脉冲激光/回波光子数Key words
polychromatic laser guide stars/continuous laser/pulse laser/return photons引用本文复制引用
刘向远,钱仙妹,朱文越,刘丹丹,范传宇,周军,杨欢..基于波长330 nm激光激发多色激光导星回波光子数的数值计算与探讨[J].物理学报,2018,67(1):120-129,10.基金项目
中国科学院大气光学重点实验室开放基金(批准号:2015JJ01)和安徽省高校和省教育厅自然科学研究重点项目(批准号:KJ2017A401, KJ2016A749).Project supported by the Open Fund of Key Laboratory of Atmospheric Optics in Chinese Academy of Sciences, China(Grant No.2015JJ01)and the Key Projects of College Natural Foundation of Anhui Province and Anhui Provincial Department of Education, China(Grant Nos.KJ2017A401, KJ2016A749). （批准号:2015JJ01）
