Origin of Self-pumped Phase Conjugate Waves in KNSBN Crystals

A multistage four-wave mixing interaction region model resulting in self-pumped phase conjugation output of the incident beam is suggested to explain the experimental observations. The competition between forward and backward two-wave mixing is demonstrated and used to explain the formation of the mechanism. The backscattering beams from random noise beams may be amplified by contradirectional two-wave mixing selectively and act as pumped beams from our experimental observations under a laser entering the negative c face of copper-doped potassium sodium strontium barium niobate crystal. The phase conjugation reflectivity of as high as 33% is measured.