1.School of Instrumentation and Optoelectronic Engineering, Beihang University, Beijing 100191, China 2.Key Laboratory of Opto-Electronic Information Science and Technology of Jiangxi Province, Nanchang Hangkong University, Nanchang 330063, China
Fund Project:Project supported by the National Natural Science Foundation of China (Grant Nos. 41776111, 61865013), the National Key R&D Program of China (Grant No. 2018YFE0115700), and the Defense Industrial Technology Development Program of China (Grant No. JCKY2019401D002)
Received Date:16 February 2021
Accepted Date:14 March 2021
Available Online:07 June 2021
Published Online:05 August 2021
Abstract:Stimulated Brillouin scattering (SBS) is a typical inelastic scattering effect generated by the interaction between intense incident laser and the acoustic wave field in medium and has always been an active research topic in nonlinear optics. The SBS can be used as a novel LIDAR technology for active optical remote sensing of temperature and sound speed structure in ocean. Although, the threshold value and gain property of SBS at normal temperature are studied, none of the threshold values and gain coefficients of SBS at different temperatures, pressures and attenuation coefficients has been investigated in detail. Further, neither the relation between threshold value and water pressure nor the relation between gain coefficient and water pressure is clear now, and little work has been reported. The theoretical and experimental studies of the influence of water parameters on the threshold value and gain coefficient of SBS are still scanty. In this paper, the effects of temperature, pressure and attenuation coefficient of water on threshold value and gain coefficient of SBS are studied theoretically and experimentally. Theoretically, the variations of threshold value and gain coefficient of SBS with temperature, pressure and attenuation coefficient are analyzed by the average attenuation coefficient method based on the distributed noise model (DNM) and coupled wave equations. The temporal waveforms of Stokes-, pump- and transmission-beam at different water parameters are obtained by using the DNM. Experimentally, a temperature-pressure controlled simulator is designed to obtain the threshold values and gain coefficients of SBS in water at different temperatures, pressures and attenuation coefficients through measuring the change of attenuation coefficient of laser pulses. The results indicate that (i) the threshold value of SBS increases with pressure increasing at the same temperature and decreases with temperature increasing at the same pressure; (ii) the threshold value is positively correlated with the attenuation coefficient at the same temperature and pressure; (iii) the gain coefficient of SBS increases with temperature increasing at the same pressure and decreases with pressure increasing at the same temperature. We also find that the temperature and attenuation coefficient have greater effect on threshold value and gain coefficient of SBS than the water pressure. The studied results are of great significance in realizing the ocean remote sensing by SBS lidar. Keywords:stimulated Brillouin scattering/ threshold value/ gain coefficient/ water parameters
SBS的噪声起振模型主要包括边界式噪声注入模型[14]、分布式噪声模型[15,16]、自发Brillouin散射噪声源模型[17]等. 为了解SBS产生过程中泵浦光、透射光及布里渊散射光能量的变化情况, 徐德[18]采用分布式噪声模型分析了非聚焦泵浦下SBS的产生, 在此基础上, 我们采用该方法对不同能量密度下泵浦光、Stokes光和透射光的波形进行了仿真, 仿真结果如图2所示. 图 2 激光器泵浦能量分别为60, 70, 80 mJ时, 泵浦光、Stokes光和透射光的波形 Figure2. Temporal waveforms of pump, Stokes and transmission laser beams at the pump energy of 60, 70, 80 mJ.