Journal of the optical society of america b-optical physics vol:11 issue:8 pages:1350-1355
We present a theory of the effects of various sources of nonlinear phase shifts or the performance of a phase-conjugate interferometer that uses degenerate four-wave mixing in the retroreflected pump-beam configuration in determining the complex (magnitude and phase) third-order nonlinear susceptibility of novel nonlinear optical materials. Our analysis reveals that the performance of the interferometer is insensitive to the net nonlinear phase shift acquired by the pump wave in a double pass through the nonlinear material. However, the interferometer is susceptible to nonlinear phase shifts through the four-wave mixing process. As a consequence, under certain conditions a finite phase is measured by the interferometer for the real third-order susceptibility of a lossless nonlinear material. This measured phase depends on the intensity imbalance between the forward and the backward pump beams as well as the intensity of the probe beam. The effects of the intensity imbalance between the pump beams on the measured phase can be compensated for by a judicious choice of the intensity of the probe beam.