Investigation of π Phase Jumps in a Ring Laser

Abstract

When a ring laser is oscillating in two counterpropagating modes, and light is reflected or scattered from one mode back into the other, it is found that the behavior of the laser can be drastically modified. In particular, certain instabilities have been encountered in which the two mode intensities oscillate in antiphase, and the phase difference between the two complex mode amplitudes exhibits jumps of ±π.^1-11 These phase jumps are always connected with zero crossings of one or the other mode amplitude. The time intervals observed between successive phase jumps show substantial variations in one of the experiments7 and in some computer simulations, whereas other computer solutions of the equations of motion indicate greater regularity.5 This discrepancy provided part of the motivation for the present work. We were also interested to see how the laser behaves when the instability condition^5-7, ^10-11 ${\tilde R_1} + \tilde R_2^* = 0,$, in which ${\tilde R_1},{\tilde R_2}$ are complex backscattering coefficients, is not satisfied exactly.