Refractive index and gain jointly-guided beam propagation and evolution inside high-power end-pumped laser medium

A self-consistent numerical model of an end-pumped solid-state laser amplifier is established. By comprehensively considering the joint guidance of the thermal-induced refractive index and gain, the propagation and evolution of the signal beam inside the gain medium are accurately simulated. The influence of the gain effect on the evolution of beam characteristics inside the crystal is investigated by adjusting the incident power. In this study, the “effective filling factor” is first proposed to accurately describe the situation of the signal beam inside the crystal. According to the theoretical analysis, it is demonstrated that the gain effect indirectly affects the deterioration of the beam quality factor M 2 by changing the effective filling factor. An end-pumped amplifier is constructed with a wavelength-tunable laser as a seed source, to separate thermal effect and gain, and the accuracy of the theoretical analysis is experimentally verified.