Efficiency of ring systems for phase self-conjugation of radiation by four-wave interaction in media with thermal nonlinearity

A theoretical analysis is made of the efficiency of typical ring systems of phase-conjugating mirrors utilizing a degenerate four-wave interaction in media with a thermal nonlinearity. The analysis is made for steady-state conditions taking into account wave saturation effects in an amplifier situated in a positive feedback circuit. It is shown that the reflection coefficient in these systems is extremely sensitive to the level of the phase-conjugate signal (as the ratio of the signal intensity to the saturation intensity of the amplifier active medium is increased, the reflection coefficient of the ring phase-conjugating mirror decreases sharply). It is also found that at a high level of the nonlinearity and for an appreciable gain per pass, these systems exhibit multistability (i.e., several different steady states exist).