Optimization of doubly Q-switched Lasers with both an electro-optic modulator and a GaAs saturable absorber

摘要

It has been proved theoretically and experimentally that a doubly Q-switched laser with both an electro-optic (EO) modulator and a GaAs saturable absorber can obtain more symmetric and shorter pulse with high pulse peak power, which is more useful in some applications. Therefore it is essential to optimize this kind of doubly Q-switched lasers. In this paper, by combining the single-photon absorption (SPA) and two-photon absorption (TPA) processes of GaAs saturable absorber, and considering the Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density as well as the influence of the electro-optic (EO) Q-switch, we introduce some new normalized parameters and provide the new normalized rate equations for a diode-pumped doubly Q-switched laser with both an electro-optic (EO) modulator and a GaAs saturable absorber, which are solved numerically. The key parameters of an optimally coupled doubly Q-switched laser are determined, and a group of general curves are generated for the first time. These key parameters include the optimal normalized coupling parameter, the optimal normalized saturableabsorber parameters, and the normalized parameters of the electro-optic (EO) Q-switch , which can maximize the output energy. Meanwhile, the corresponding normalized energy, the normalized peak power and the normalized pulse width are given. The curves clearly show the dependence of the optimal key parameters on the parameters of the gain medium, the GaAs saturable absorber, the electro-optic (EO) Q-switch, the resonator and the spatial distributions of the intracavity photon density. These optimal results are compared with those of the optimized single Q-switched lasers. Sample calculations for a diode-pumped Nd:YVO_4 laser with both an electro-optic (EO) modulator and a GaAs saturable absorber are presented to demonstrate the use of the curves and the relevant formulas.