COOPERATIVE FREQUENCY LOCKING AND TRISTABILITY IN A CLASS-B LASER

The locking and unlocking phenomena of the modes of the transverse fam ily q = 1 in a CO2 laser are investigated. The experimental results sh ow three characteristic regions: a bistability between two helical wav es of opposite handedness, a tristability among the two helicities of opposite handedness and an unlocked state, and the unlocked state. Nea r the locking threshold, oscillations which can be interpreted as due to the oscillations of the modal amplitudes and relative phase are als o observed. These results are found to be consistent with solutions of the two-mode Maxwell-Bloch equations for class-B lasers.