Phase-locked phase conjugation using a Brillouin loop scheme to eliminate phase fluctuations

We describe experiments investigating a technique that uses stimulated Brillouin scattering to phase conjugate a number of laser beams while preserving their relative phases. Phase locking of a number of beams focused into a stimulated Brillouin scattering cell is achieved by four-wave mixing with a pair of unfocused pump beams. The second pump is generated from the first by use of a stimulated Brillouin scattering loop geometry that minimizes phase fluctuations. We show that the reduction in phase fluctuations substantially improves the degree of phase locking. The requirements on four-wave mixing pump intensity are determined. The technique has the advantage of being insensitive to changes in alignment, with the potential to combine coherently a large number of laser amplifiers in a simple and compact geometry.