SBS suppression of amplified spontaneous emission in high-gain amplifiers

Summary form only given. Optical phase conjugation using stimulated Brillouin scattering (SBS) is widely used in high-average-power solid-state lasers and multipass amplifiers for correction of problems brought on by thermally induced birefringence and depolarization and for pulse compression. Diffraction-limited beams are now routinely obtained in 100 W average-power high-repetition-rate Nd:YAG laser systems where a SBS mirror is an integral part of the system. In these applications, the pump lasers used all have narrow bandwidths, typically <1 GHz. The reason for this is well-known in that the SBS threshold for a noisy (multi-frequency) pump is higher than that for a single-longitudinal-mode pump or one with just a few modes. So, in order to obtain high reflectivity using minimal power for the SBS mirror, narrow-bandwidth lasers are used. We have taken note of this property of SBS and explored its utility to solve another important problem in laser amplifiers: the suppression of amplified spontaneous emission.