Spectroscopic and energy-transfer parameters for Er^3+-doped and Er^3+, Pr^3+-codoped GeGaS glasses

Abstract

The absorption and emission spectra and the rate parameters for the important energy-exchange processes relevant to the ${ }^4{I}_{11/2} \to { }^4{I}_{13/2}$ laser transition in ${\mathrm{Er}}^{3+}$-doped and ${\mathrm{Er}}^{3+},$ ${\mathrm{Pr}}^{3+}$-codoped GeGaS glasses are presented. The rate parameters are determined after optical excitation with a tunable pulsed optical parametric oscillator that excites the ${ }^4{I}_{11/2}$ and ${ }^4{I}_{13/2}$ energy levels directly. For the ${\mathrm{Er}}^{3+}$ singly doped samples, the energy-transfer upconversion (ETU) macroscopic rate parameters for the upper and lower laser levels were measured for a range of ${\mathrm{Er}}^{3+}$ concentrations. In correspondence with ZBLAN and the fluoride crystals, the ${(}^4{I}_{13/2},{ }^4{I}_{13/2})\to {(}^4{I}_{9/2},{ }^4{I}_{15/2})$ ETU process of the lower laser level is measured to be stronger than the corresponding ETU process of the upper laser level. Such a condition enables energy recycling to occur. A higher rate of energy transfer from the ${ }^4{I}_{13/2}$ level of ${\mathrm{Er}}^{3+}$ to ${\mathrm{Pr}}^{3+}$ deactivator is measured as compared with the corresponding energy transfer from ${ }^4{I}_{11/2}$ level to both the ${\mathrm{Pr}}^{3+}$ deactivator and OH impurity. With these favorable energy-transfer conditions, the prospect for the future development of highly efficient ∼3-µm fiber lasers with GeGaS glass as the host material is excellent.