Spatio-temporal nature of the optical return field generated by four-wave mixing in photorefractive and Kerr materials

We have theoretically analyzed the return field produced by an externally pumped Kerr medium, an externally pumped photorefractive medium, and a self-pumped photorefractive medium, for an input field with arbitrary spatial and temporal characteristics. For a stationary beam with spatial structure, all three cases yield a spatial phase-conjugate return beam. For a beam with dynamic fluctuations, each case returns a field with different temporal character. For the case of a self-pumped photorefractor, it is found that the dynamics of the return beam are represented by a conventional reflection rather than a temporal phase conjugate. While this geometry may have been thought of as a simple way to provide phase-conjugate feedback for dynamic stabilization in semiconductor lasers, an in-depth analysis shows that our theoretical findings agree with previously reported experimental results. © 2002 Optical Society of America OCIS codes: 190.5330, 190.5040, 140.5960.