Upconversion of 5I7 to 5I6 and 5I5 in Ho:YAG and Ho:YLF

Recent developments of 2 µm lasers with Tm, Ho and Tm/Ho doped materials indicate that at high inversion levels loss due to upconversion of excited ions in the upper laser level becomes significant. Although some attempts have been made to characterize these loss mechanisms1·2, indirect pumping of the upper laser level was used in these studies. To measure the upconversion rate it requires a detailed knowledge of the excited state densities. In this study, the Ho ions are selectively excited to 5I7 to create a uniform distribution of excited ions and emissions from higher excited states are monitored as a measure of the upconversion processes.