Modeling of a Q-switched master oscillator power amplifier fiber laser and gain saturation properties

Abstract

Here, a model is developed for a master oscillator power amplifier of a Q-switched double-clad ytterbium–doped fiber laser, based on time-dependent coupled rate equations by virtue of the finite difference method. At first, the master oscillator is modeled with various rise times and its effect on the output peak power and pulse duration is investigated. The output pulse is characterized in terms of input pump power, dopant concentration, fiber length and core diameter. Then, the power amplifier (PA) is modeled to determine the input/output signals via the numerical solution of the coupled rate equations. The best fitting of data is performed over the analytical amplification relation by making use of the least squares method in order to find the gain and saturation parameters. Eventually, the small signal gain and saturation power are obtained under various parameters such as input pump power, dopant concentration, fiber length and core diameter. The dominant effect of filling factors are also discerned versus core diameters to attain the single mode operation. Finally, the power extracted from a single stage PA is envisaged versus various parameters.