Measurement of the threshold of nonfocusing-pumped stimulated Brillouin scattering based on the spatial characteristic of the reflected pulse

摘要

We present a method for measuring the threshold of stimulated Brillouin scattering (SBS) when a large-aperture laser pulse with ultra-Gaussian shape is used as the pump source. By using an optical aperture to filter out part of the backward scattered light, the measured energy efficiency will be conserved below the SBS threshold and nonconserved above the SBS threshold. Based on the differences between the two conditions we can judge whether the pump intensity is above the SBS threshold or not by analysis of the energy efficiency of the system. The experiment is carried out with an Nd:YAG laser, delivering an ultra-Gaussian-shaped pulse with the pulse width of 3 ns, beam diameter of about 20 mm, and wavelength of 527 nm. Heavy fluorocarbon liquid FC-770 is adopted as the nonlinear medium. The measured SBS threshold under this condition is 634 MW/cm(2) and it has a good correspondence with the theoretically calculated results. (C) 2019 Optical Society of America