Optimization of fiber-coupled laser-diode end-pumped lasers: Influence of pump-beam quality

A general model has been developed for the optimization of fiber-coupled laser-diode pumped lasers by including the effect of pump-beam quality into the mode-overlap integrals. The numerical results of the mode-overlap integrals have been fitted to an analytical function of pump spot size, laser mode size and the parameter β, which is in terms of laser-diode beam quality and properties of the active medium. This analytical function allowed us to obtain explicit formulae for the threshold pump power, the slope efficiency, and the optimum pump spot size. With these formulae, the optimum mode size and the maximum output efficiency can be easily calculated for arbitrary values of β and input power. From the numerical results, we obtained an analytical expression to relate the required input power and pump-beam quality to the desired output efficiency mod properties of an active medium. The present model provides a straightforward procedure to design the laser resonator and the optical coupling system for optimization. To illustrate the utility of the present model, a Nd:YAG laser pumped by fiber-coupled laser diodes is considered and optimized.