Pulse Formation, Harmonic Mode-Locking, and Stability in Actively Mode-Locked Laser Cavities

Theory and simulations of the mode-locking dynamics in an active cavity driven by an acoustooptic modulator is considered. Three solution types and their stability are considered: plane-waves, solitons, and periodic pulse trains. By tuning the gain pumping in the cavity, all three solution types are exhibited with the transition in stability between each of these operating states characterized by a modulated wavetrain ( Q-switching-like) behavior. Two key parameters are critical for enhancing performance: the ratio of the acoustooptic modulation period to the cavity round-trip time and the degree of localization of the acoustooptic modulation. A complete classification of the behavior is given for these two critical effects as a function of the cavity gain saturation. Enhanced performance can be achieved with a high degree of localization in the modulator and for a modulation period commensurate with the round-trip cavity time.