Kinetics of the evolution of an absolute instability due to the Brillouin nonlinearity under four-wave mixing conditions

A four-wave hypersonic phase-conjugate mirror was proposed and implemented to observe the evolution of an absolute instability under conditions of continuous variation of the wave mismatch δk. Kinetic equations describing four-wave mixing under conditions of an absolute instability of counterpropagating reference waves are solved numerically taking into account the group delay effect. Strong modulation of all the waves at the exit from a medium of length L is predicted theoretically and observed experimentally when δkL = 0. This disappears with increasing wave mismatch δkL ≈ 2π. Estimates are obtained of the maximum theoretical sensitivity and the maximum reflection coefficient of the signal wave incident on such four-wave hypersonic phase-conjugate mirrors.