Theory of Q switching in actively mode-locked lasers

An analytic theory is proposed that characterizes Q switching in an active mode-locked cavity as the nonlinear interaction of two unstable modes: one symmetric, another antisymmetric. The phase difference between these modes generates a nonlinear beating interaction that gives rise to quasi-periodic behavior in the laser cavity. This quasi-periodic behavior is responsible for the Q-switching phenomenon and is controlled by the interaction and overlap between neighboring pulses. With a linear stability analysis, a simple qualitative description of the Q-switching phenomenon is given that is verified with numerical simulations of the governing active mode-locked equations. This model characterizes the Q switching as a function of the physical parameters of the laser cavity and elucidates the mechanisms for controlling its behavior.