Mechanisms for internally self-pumped phase-conjugate emission from BaTiO_3 crystals

Detailed measurements of the self-pumped phase-conjugate emission that arises from internal reflections within crystals of BaTiO3 have been made. Four-wave mixing, possibly enhanced by stimulated photorefractive scattering around loops of light internally generated within the crystal, and four-wave mixing at coupling regions of a ring cavity set up between diagonal corners of the crystal are two mechanisms believed to give rise to phase-conjugate beams. An explanation is also given for the unstable effects often observed on the phase-conjugate beam and that give rise to frequency shifts, pulsations, and oscillations. The power of the beam incident upon the crystal determines the threshold characteristics for self-pumped phase-conjugate emission.