Fidelity of Brillouin amplification with Gaussian input beams

Abstract

The process of Brillouin amplification when the input pump and signal beams have Gaussian spatial profiles is investigated. Two distinct regimes are considered. In the small signal regime, it is shown that the signal beam undergoes spatial beam narrowing as it propagates through the amplifier owing to the exponential dependence of signal beam gain on pump beam intensity. The relative change in spot size is found to depend on both the peak signal intensity gain and on the input signal to pump spot size ratio. In the large signal (depleted pump) regime, it is found that the signal beam becomes broadened if the pump depletion is significant and the output spot size depends on the input signal beam intensity. The theoretical predictions are verified experimentally using a Q-switched Nd-YAG laser to provide pulses of 30 ns FWHM duration and wavelength 1.06 micrometers , and using CCl2FCCIF2 as the nonlinear medium.