Fluorescence reabsorption and its effects on the local effective excitation lifetime

A spectral theory of fluorescence reabsorption is presented that allows us to describe the effects of radiation trapping, which especially occurs in barrel-polished laser rods, as an effective change of the excitation lifetime. This effect causes a local fluorescence lifetime difference in the laser medium and thus a local change in the quantum efficiency. The theory is compared to experimental results obtained with an Er³⁺:YAG rod with good agreement.