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

The absorption and emission spectra and the rate parameters for the important energy-exchange processes relevant to the 4I11/2 → 4I13/2 laser transition in Er3+-doped and Er3+,Pr3+-codoped GeGaS glasses are presented. The rate parameters are determined after optical excitation with a tunable pulsed optical parametric oscillator that excites the 4I11/2 and 4I13/2 energy levels directly. For the Er3+ singly doped samples, the energy-transfer upconversion (ETU) macroscopic rate parameters for the upper and lower laser levels were measured for a range of Er3+ concentrations. In correspondence with ZBLAN and the fluoride crystals, the (4I13/2, 4I13/2)→(4I9/2, 4I15/2) 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 4I13/2 level of Er3+ to Pr3+ deactivator is measured as compared with the corresponding energy transfer from 4I11/2 level to both the Pr3+ 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.