Er-doped sesquioxides for 1.5-micron lasers - spectroscopic comparisons

Due to the favorable thermal properties of sesquioxides as hosts for rare earth laser ions, we have recently studied the spectroscopy of Er:Lu2O3 in the 1400-1700 nm wavelength range, and here report its comparison with our earlier results on Er:Y2O3 and Er:Sc2O3. These studies include absorption and fluorescence spectra, fluorescence lifetimes, and inference of absorption and stimulated emission cross sections, all as a function of temperature. At room temperature, optical absorption limits practical laser operation to wavelengths longer than about 1620 nm. In that spectral range, the strongest stimulated emission peak is that at 1665 nm in Er:Sc2O3, with an effective cross section considerably larger than those of Er:Y2O3 and Er:Lu2O3. At 77K, the absorption is weak enough for efficient laser operation at considerably shorter wavelengths, where there are peaks with much larger stimulated emission cross sections. The three hosts all have peaks near 1575-1580 nm with comparably strong cross sections. As we have reported earlier, it is possible to lase even shorter wavelengths efficiently at this temperature, in particular the line at 1558 nm in Er:Sc2O3. Our new spectroscopic studies of Er:Lu2O3 indicate that its corresponding peak, like that of Er:Y2O3, has a less favorable ratio of stimulated emission to absorption cross sections. Reasons for the differences will be discussed. We conclude that for most operating scenarios, Er:Sc2O3 is the most promising of the Er-doped sesquioxides studied for laser operation around 1.5-1.6 microns.