PHASE DEFECTS IN A PHASE-CONJUGATE PHOTOREFRACTIVE-GAIN OSCILLATOR

We have performed experiments to establish the origin of phase defects in a phase-conjugate cavity composed of a curved mirror of high reflectivity and a phase-conjugating mirror based on four-wave mixing in photorefractive BaTiO3 pumped by counterpropagating Ar+ laser beams. An intracavity diaphragm was used to change the Fresnel number, thus providing the observation of different transverse structures in the output plane of the photorefractive oscillator.