Antiphase Q-switch dynamics in a multimode solid-state laser with saturable absorber

Antiphase Q-switch dynamics in a multimode solid-state laser with saturable absorber is investigated both experimentally and theoretically. The system under study is a large cavity, longitudinally pumped Nd:YAG laser with Cr4+:YAG as saturable absorber. Asymmetric two-mode operation was found for a wide range of control parameters. To describe the sparse mode distribution, a multimode rate equation system was developed that accounts for spatial grating in the active medium and non-linear absorption. The model is shown to predict pulse sequences experimentally observed as the pump parameter is changed. For high pump ratios a quasi-pure periodic antiphase state is recovered which consists of two modes pulsing with the same period T and shifted by T/2. It is then conjectured that an apparent symmetry of the system can be established for certain values of the control parameters. (C) 1999 Elsevier Science B.V. All rights reserved.