Pulse-energy dynamics of passively mode-locked solid-state lasers above the Q-switching threshold

Abstract

We have investigated the dynamical behavior of various passively mode-locked solid-state lasers by measuring how a modulation of the pump power affects the output power. We show theoretically and experimentally how the damping of the relaxation oscillations is reduced and finally becomes zero when the pump power is reduced so that the threshold for Q-switched mode locking is approached. For the first time to our knowledge, this method provides important information on the stability of mode locking above the Q-switched mode-locking threshold. It is applicable to lasers that are mode locked with slow-saturable absorbers. The results helped to explain the cause of unexpectedly low Q-switching thresholds in two cases. Also we obtain some useful spectroscopic information.