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Annual Meeting Optical Society of America

Spatial coherence of a phase conjugate wave generated by stimulated Brillouin scattering

Timothy R. Gosnell, David E. Watkins

Published Jan 1, 1986• 0 citations

Abstract

We have measured the spatial coherence of an initially fully spatially coherent pump laser beam following stimulated Brillouin scattering (SBS) in SF6 gas at 15 atm. Using a simple interferometric technique, we find that the fraction of the diameter of the scattered beam which is spatially coherent decreases with increasing f/No. of the incident 308-nm pump beam. Surprisingly, we also find that the spatial coherence of the scattered beam increases with decreasing pump energy. To our knowledge, these measurements are the first to address the issue of spatial coherence in SBS and point toward an important measure of the fidelity of phase conjugation produced by SBS. The influence of a weak seed beam on the coherence of the phase conjugate beam is also discussed.

DOI: 10.1364/oam.1986.tui2

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We have measured the spatial coherence of an initially fully spatially coherent pump laser beam following stimulated Brillouin scattering (SBS) in SF6 gas at 15 atm. Using a simple interferometric technique, we find that the fraction of the diameter of the scattered beam which is spatially coherent decreases with increasing f/No. of the incident 308-nm pump beam. Surprisingly, we also find that the spatial coherence of the scattered beam increases with decreasing pump energy. To our knowledge, these measurements are the first to address the issue of spatial coherence in SBS and point toward an important measure of the fidelity of phase conjugation produced by SBS. The influence of a weak seed beam on the coherence of the phase conjugate beam is also discussed.

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.

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