Spectroscopic properties and energy transfers in Tm3+ singly- and Tm3+Ho3+ doubly-doped glasses

Abstract Spectroscopic measurements and analysis of energy transfer processes for Tm 3+ singly- and Tm 3+ Ho 3+ doubly-doped glasses pumped with 790 nm diode laser have been performed. The emission cross-sections and the net gain have been determined from the measured absorption spectra for both the ions on the basis of principle of reciprocity. Tm 3+ singly-doped fluorozircoaluminate glass, which has a higher fluorescence efficiency at 1.82 μm and a longer upper state lifetime, is a material suitable for Tm laser compared with oxide glasses. The quantum efficiency of Ho 3+ fluorescence of 5 I 7  5 I 8 at 2.05 μm for the Tm 3+ Ho 3+ doubly-doped glass is dominated by three energy transfer processes: Tm 3+ Tm 3+ cross-relaxation, net Tm 3+ Ho 3+ energy transfer, and energy transfer upconversion. The first process allows pumping efficiency to approach 2, and the second one contributes to population of the upper 5 I 7 laser level, while the final process gives rise to a sublinear increase in upper state population with pump power. Optimum doping levels for laser performance are easily predicted based on spectroscopic measurements and are found to be 2–8Tm 3+ (10 20 /cm 3 ) for Tm 3+ singly-doped and 2–8Tm 3+ /0.3–1Ho 3+ (10 20 /cm 3 ) for Tm 3+ /Ho 3+ doubly-doped systems, respectively.