Double phase conjugation in media with a local response

An analysis is made of double phase conjugation in media with a local response. A threshold is found for the generation of a phase-conjugated wave by the double process in a medium with a local response and with additional amplification. An analysis is made of the further possibilities of generation of phase-conjugated radiation in the case of a four-wave interaction characterized by a feedback loop established when double phase conjugation takes place in a nonlinear medium. The threshold intensity of the input radiation ensures possible generation of a phase-conjugated wave as a result of a four-wave interaction characterized by a feedback loop and merging of counterpropagating beams in a nonlinear medium.