Picosecond degenerate two-wave mixing

Abstract

We examine transient, degenerate two-wave mixing by using picosecond laser pulses to create orientational index gratings. A phase shift between the electromagnetic and material index gratings can be created with degenerate laser beams through nonlinearities that exhibit a finite response time. This requires that the response time for the nonlinear material and the laser pulse time be compatible. The specific mechanism for phase shift arises from the time delay that the nonlinear material exhibits to incident laser pulses, and it serves as a mechanism for energy transfer. We have examined this phenomenon experimentally in CS2 and found good agreement between theory and experiment. The theory has been extended to treat situations in which the medium is irradiated by very high power pulse beams, and the saturation characteristics of this phenomenon have been determined. Additionally, the change in laser pulse shape and the detailed physical characteristic of the optical index gratings responsible for energy transfer for saturation conditions have been investigated.