Optimization of pulse width of double passively Q-switched lasers with GaAs and Cr-doped saturable absorbers

Compared with a single passively Q-switched laser, a double passively Q-switched laser with a GaAs saturable absorber and a Cr⁴⁺-doped saturable absorber can produce more symmetric and shorter pulses with high pulse peak power. New normalized coupled rate equations for a double passively Q-switched laser with both a GaAs saturable absorber and a Cr⁴⁺-doped saturable absorber are solved numerically, where the single-photon absorption (SPA) and two-photon absorption (TPA) processes of GaAs are combined. The Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density are considered. The optimization of a double passively Q-switched laser to obtain the shortest pulse width is performed, and a group of general curves are generated for the first time. The curves clearly show the dependence of the optimal normalized parameters on the parameters of the gain medium, the GaAs saturable absorber, the Cr⁴⁺-doped saturable absorber and the spatial distributions of the intracavity photon density. Sample calculations for a diode-pumped Nd³⁺:YVO₄ laser with both a GaAs saturable absorber and a Cr⁴⁺:YAG saturable absorber are presented to demonstrate the use of the curves and the related formulas.