Laser mode selection with slowly opened Q switches

Giant pulse lasers with slowly opened switches have experimentally been demonstrated to have a significantly lower beam divergence than the same laser with a quickly opened switch. The two types of slowly opening switch in most common use are rotating prisms and Faraday rotators. In this paper the pulse buildup with a Faraday-rotator switch is analyzed and it is shown that an optimum condition exists where the laser will match the switch with negligible loss in the slow switching. Experiments are then reported in which this analysis is confirmed in detail by comparing the measured output linewidth with that expected from an analysis of the resonant reflector used, and results derived from the experimental power-tuning curve. The far-field spatial distribution was Lorentzian with a full width at half-peak intensity of rad and was caused by the scattering in the average-quality ruby rod used.