Rippling of the critical surface by four-wave processes in a laser-irradiated plasma

Rippling of the critical surface is investigated by a four-wave process in which two electromagnetic waves are scattered by an ion perturbation for very high intensities in a laser-irradiated plasma. The mechanism is the parametric oscillating two-stream instability for the electromagnetic waves. The instability grows in the direction of the laser magnetic field; however, it hardly grows in the direction of the laser electric field. The thresholds and growth rates are obtained by a phase-integral method, and there are optimized wavenumbers and pump fields for the growth. Results of two-dimensional fluid and three-dimensional particle calculations agree with the theoretical predictions. The theory also seems to be consistent with the observations in laser experiments.