Brillouin enhanced four-wave mixing with the liquid fluorocarbon

Abstract

Stimulated Brillouin Scattering (SBS) is a nonlinear optical effect that is broadly used for correcting the beam quality of laser beams, their mode control, amplification and phase conjugation. Two factors are essential when it comes to selection of the nonlinear medium for SBS, its efficiency or gain coefficient and safety. For example, a low SBS gain coefficient in the fluorocarbon liquid C8F18 is at least one order of magnitude lower than other nonlinear media, typically limits its application in high-power laser systems. However, highly purified C₈F₁₈ is a very safe and stable nonlinear medium, and in combination with its high optical breakdown threshold, has become attractive for many practical applications. This paper discusses a phase conjugate mirror (PCM) using the SBS effect in C₈F₁₈. A PCM reflectivity of better than 90% has been achieved in an optimized experimental geometry of the incoming beam. The output energy of the phase conjugated pulse linearly increased with the energy of the input pulse beyond a threshold level of about 3.3 mJ. The estimated slope efficiency is about 95%. For weak signal amplification, we have realized greater than 105 amplification with Brillouin enhanced four wave mixing (BEFWM) with an input signal at the level of several nJs. A reflected energy as high as 11 mJ has been achieved with a 400 μJ incoming input signal. Further lowering of the signal energy should result in a higher amplification.