Optimization in scaling fiber-coupled laser-diode end-pumped lasers to higher power: Influence of thermal effect

The optimum mode-to-pump ratio in scaling fiber-coupled laser-diode end-pumped lasers to higher power has been investigated by including the thermal effect into the space-dependent rate equation analysis. The optical path difference (OPD) distribution has been derived as a function of the pump-beam quality, focus position of pumping light, and pump radius at the focal plane under the assumption that the end faces of the crystal are thermally insulated. The diffraction losses arising from thermally induced spherical aberration have been estimated by the Strehi intensity ratio, The present results for the optimum node-to-pump ratio is markedly different from the previous results In which thermal effects are neglected and the optimum mode-to-pump ratio is an increasing function of input pump power, It is seen that the optimum mode-to-pump ratio a decreasing function of input pump power, Also, the optimum mode-to-pump ratio is less than unity in the ease of a slightly high pump power. The practical example of a Nd:YAG laser pumped by a 13-W fiber-coupled laser diode is considered to confirm our physical analysis.