Evaluation of amplified spontaneous emission in thin disk lasers using the spectral linewidth.

Amplified spontaneous emission (ASE) is important to power scaling of the large-scale, high-gain thin disk laser. In this paper, spectral properties of ASE in Yb:YAG thin disk lasers are deeply studied in both theory and experiment. The experimental results show that the ASE strength is much stronger when emitted from the edge surface than the pumping area. And the spectrum of ASE emitted from the coarsened edge surface is angle independent. Meanwhile, the reabsorption effect in the Yb:YAG crystal on spectral linewidth is analyzed and corrected. Finally, ASE spectral linewidths have been measured. We demonstrate that the spectral linewidths can evaluate ASE strength effectively.