Control of Q-switched mode locking by active feedback

Summary form only given. Since the early days of passive mode-locking additional undesired Q-switching is a major concern. Especially in the case of fiber and solid-state lasers with long upper-state lifetimes mode-locked by semiconductor saturable absorbers Q-switched mode locking is difficult to suppress. Stability criteria for the suppression of Q-switching instabilities in passively mode-locked lasers using a variety of absorber characteristics have been derived. These stability criteria show that there exists a limited parameter-range (i.e., pump power, absorber saturation, modulation depth of the absorber, pump volume and gain cross section,...) where the laser is continuous wave (CW) mode-locked. In the paper we show, that the Q-switching instability in Nd:YVO/sub 4/ mode-locked lasers can be controlled for a large variety of laser systems by intracavity loss or gain-modulation driven by the output of the laser via a feedback loop.