Abstract

From experiments with Q-switched solid state lasers it is known that a typical repetition rate exists, being characteristical for the employed laser crystal. If the actual repetition rate is below this value the pulsewidth τ is small but the average power $\overline{P}$ decreases, while for a higher repetition rate the pulses become broad and $\overline{P}$ increases. The first case is preferable in order to achieve high peak powers, and crystals with a long fluorecence lifetime like Nd:YLF are the preferable choice. Nevertheless, for applications like marking or drilling the repetition rate is of high interest because it increases the processing speed. Investigating the three classical crystals Nd:YAG, Nd:YVO₄, and Nd:YLF under comparable circumstances we found, that in a plot of the ratio $\overline{P}/\tau$ vs. the repetition rate v a maximum occurs. This maximum corresponds to the repetition rate at which the conversion efficiency of the external frequency doubling process becomes maximal and processing effect on metallic surfaces stays considerable. Upon the rate-equation based Q-Switch theory described in References (1,2) we are able to explain the experimental laser-behaviour illustrated in figure 1. Furthermore, predictions for other four-level solid-state laser hosts can be made and conclusions concerning the crystal quality can be drawn.

© 1998 IEEE