High-efficiency pulsed 106-μm phase-conjugate reflection via degenerate four-wave mixing

Abstract

We present the first reported observation in the infrared of nonlinear phase-conjugated reflection. This was achieved via degenerate four-wave mixing in polycrystalline germanium. The observation was facilitated by taking advantage of the counterpropagating (strong) waves internal to a pulsed CO2 laser cavity. The measured effective reflectivity was 2% with a 10-mm interaction length. This simple intracavity technique is generally applicable to any nonlinear material transparent at the wavelength of the laser into which it is inserted.