Hysteresis effects in the two-mode dye ring laser

By inserting an optical diode consisting of Faraday and quartz rotators into the cavity of a dye ring laser and by applying a sinusoidal current at 10 Hz to the Faraday rotator, we have been able to observe hysteresis in the intensity of each counterpropagating laser mode. The hysteresis results from the laser's attempts to switch among metastable states in response to the external stimulus. We have studied the hysteresis as a function of laser pump parameter a and find that it starts when a exceeds about 25, reaches a peak when a is about 60, and becomes small when a exceeds about 70. At this stage the laser is unable to respond because of the high potential barrier between metastable states. The results are in general agreement with computer solutions of the equations of motion and are related to recent work on stochastic resonance in a dye ring laser.