We present simulations of thin-disk amplifiers considering amplified spontaneous emission (ASE), as the ASE can have a crucial influence on achievable gain, especially for high energy, medium rep-rate pulse amplifiers. The model needs to incorporate the full spatial distribution of inversion and - due to the quasi-3-level nature of the typical active ion Yb3+, i.e. the temperature dependence of effective cross sections - the temperature distribution in the thin disk. ASE-photon flux has to be resolved with high spatial and spectral resolution to incorporate the spectral emission distribution . Furthermore, we also need to take into account the radiation guiding effect of the thin disk, i.e. the multiple reflections of ASE and fluorescence at the back- and front side of the disk . Due to the significantly non-linear dependence between inversion and ASE, a transient model, reproducing the temporal evolution of absorbed pump power, amplified laser power and ASE-photon flux is required . A fast implementation in Python allows us optimizations with variations on large parameter sets in the future.
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