Spontaneous oscillations of the angle of rotation of the radiation polarization in a double-pass amplifier

It is shown that an instability of the rotation of the direction of polarization of the output radiation may occur in double-pass amplifiers operating under saturation conditions. This instability appears because of a nonlinear interaction between the opposite waves in an amplifier. A model of relaxation constants for different types of transition is used to derive criteria for the occurrence of such an instability.