Influence of water parameters on threshold value and gain coefficient of stimulated Brillouin scattering

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.