Noise-free phase conjugation of high power single mode laser beams by stimulated Brillouin scattering

Abstract

Exact self-phase conjugation of laser beams by stimulated Brillouin backscattering is well known to arise when the incident laser field exhibits a spatially multimode structure. Here will be shown that single mode laser beams can be phase conjugated only at powers lower than their beam break-up threshold. Furthermore we shall experimentally demonstrate a new way of generating a phase conjugate wave of single mode laser beams at powers higher than the self-focusing threshold by two or three orders of magnitude. It consists of interferometrically splitting the pump laser beam into four components of equal intensities. Their wave-vectors lay out along the edges of a tetragonal basis pyramide: the bi-periodic interference patterns of these four place waves generates diffraction-limited stimulated Brillouin emission with good beam stability and reproducibility.