Numerical analysis of amplified spontaneous emission of thin disk laser with adjustable ring pump spot

The amplified spontaneous emission (ASE) effect is a major factor affecting large size, high-gain Yb:YAG thin-disk lasers. In this paper, considering the reabsorption effect of the quasi-three-level Yb:YAG crystal, an adjustable ring pump spot (ARPS) is proposed to suppress the ASE effect for the high power multimode thin-disk lasers. A numerical integration model is built to calculate the output power density, the distribution of ASE photon flux density, and the gain coefficient of the ARPS. Compared with the circle pump spot and the hollow pump spot, the reabsorption effect in the ring shaped unpumping region of the ARPS has a good balance between the ASE photon amplification in the pumping areas and attenuation in the unpumping area of the thin-disk crystal. Significant improvement of suppression ability of the ASE effect can be achieved by using the ARPS with an optimal position of the ring-shaped unpumping area, especially for the larger pump spot.