Passively q–switched quasi–three–level laser and its intracavity frequency doubling

A passively Q–switched quasi–three–level Nd:YAG laser is intracavity frequency doubled to generate a blue laser. The 473–nm blue laser has a peak power of 37 W and a pulse width of 23 ns at a pumping power of 1.6 W. To model this laser numerically, we developed rate equations by taking into consideration both the quasi–three–level nature of the gain medium and the four–level nature of the saturable absorber. Good agreement was achieved between experimental and simulated results for both the fundamental and the second-harmonic output. The reabsorption loss of the gain medium is estimated under pulsed operation. © 2002 Optical Society of America.