Excited-state dynamics including radiative diffusion in quasi-three-level laser crystals: application to Yb^3+-doped Y3Al5O12

I present a model devoted to linking the properties of a quasi-three-level laser crystal to microscopic parameters. The role of the radiative diffusion is taken into account with a sample-size-dependent parameter, including the total internal reflections, allowing both radiative and nonradiative diffusions to be treated equally. The radiation self-trapping aspect is quantified with the number η′imp of imprisoned photons engendered by one absorbed pump photon. The losses toward the traps that are not always well known are described with the dipole-dipole interaction, giving a microscopic interpretation of the heat dispensed in the sample from the pump. One prediction is that the excited-state decay of the donor subsystem is exponential, in agreement with experiment. The main experimental data, which are the excited-state intrinsic and extrinsic lifetimes τ and τ′ and the extrinsic fractional thermal loading ξ′, can be calculated by adjusting a small number of parameters. This number can be reduced by use of spectroscopy. I have shown that this model can be applied with a reasonable success to Yb3+-doped Y3Al5O12.