The effect of Nd concentration on the spectroscopic and emission decay properties of highly doped Nd:YAG ceramics

Abstract

High-resolution optical spectroscopy shows that no additional defects or large-scale deformations take place in Nd:YAG ceramics doped with up to 9 at. % Nd as compared to the diluted single crystals. Spectral satellites connected with ensembles of Nd ions, predicted by the statistics of a random distribution over the available lattice sites, are observed at low temperatures. At higher temperatures the resolution is lost and these ensembles contribute to an inhomogeneous broadening of the lines. At room temperature the global emission decay of ${}^{4}{F}_{3/2}$ is nonexponential and can be explained by the common effect of a direct donor-acceptor transfer process with parameters determined earlier for diluted crystals and by a migration-assisted transfer whose ensemble-averaged rate depends quadratically on the Nd concentration ${C}_{\mathrm{Nd}}.$ The calculated quantum efficiency \ensuremath{\eta} and the figure of merit $\ensuremath{\eta}{C}_{\mathrm{Nd}}$ indicate that concentrated Nd:YAG components are suitable for continuous-wave laser emission and, coupled with resonant hot band pumping into the emitting level, they show the prospect for scaling Nd:YAG lasers to very high powers.