Abstract

A growing demand for narrow-linewidth laser sources with high average output power for scientific, industrial and military applications has pushed the development of ytterbium doped large mode-area (LMA) fiber amplifiers to more than 400 W of output power with nearly diffraction limited beam quality [1]. Stimulated Brillouin scattering (SBS) was successfully suppressed by pump induced thermal gradients along the fiber that shift the center frequency of the Brillouin gain spectrum and lower the effective Brillouin gain. In this contribution for the first time to our knowledge thermal deformations of Brillouin scattering spectra were experimentally detected with a heterodyne system during operation of a high-power fiber amplifier and theoretically described using a numerical rate-equation model [2]. At low signal intensities the Brillouin gain spectrum was determined with a pump-and-probe measurement [2]. A deeper understanding of the Brillouin scattering spectral evolution in fiber amplifier systems will help to increase the power level into the kW range.

© 2009 IEEE