Modeling the intra-cavity frequency-doubling of a diode pumped Nd3+ laser/KTP passively Q-switched with GaAs

A mathematical model describing the dynamic emission of the intracavity frequency-doubling of a Q-switched Nd3+ - laser/KTP with GaAs semiconductor saturable absorber has been developed. The model is used to describe the temporal behavior of the laser, absorber and KTP system, in which the mutual interaction and effect between photons of the pumping laser pulse, GaAs semiconductor saturable absorber and crystal coupling has been taken into account. The suggested model allows us to study the impact of the variations of the input pumping laser powers (pumping rate, maximum amplification coefficient and loss coefficient) on the output pulse power characteristics of the Nd3+ - laser/KTP. The calculations in this work show that two-photon absorption and free-carrier effects play an important role in the formation of the output laser pulse. The nonlinear losses in GaAs can limit the obtainable pulse power. The calculations also show the broadening of the output pulse of the Q-switched Nd3+ - laser/KTP.This suggested model estimates the optimized values of the relative population inversion, threshold population, density of peak maximum and pulse width, and the relation between initial and final relative population inversion is obtained. The calculated results are in good agreement with the available experimental data. (author)