Low-threshold lasing at 1975 nm in thulium-doped tellurite glass microspheres.

Thulium-doped (Tm-doped) tellurite glass microspheres are used as laser media. Emission lines at wavelengths near 1975 nm are observed. The onset of laser emission is achieved with 8.6 and 30 μW of coupled pump power and injected pump power, respectively, at a wavelength of 1554 nm. To the authors' knowledge, these are the lowest laser threshold values recorded for a Tm-doped tellurite glass microcavity. Intrinsic Q-factors above 10(6) for the undoped tellurite glass microspheres assert the quality of the fabrication processes. An optical intrinsic Q-factor comparison between Tm-doped tellurite and undoped tellurite microspheres shows that ion absorption is the dominant loss source at pump wavelengths. Lower lasing threshold powers and higher power conversion are observed at longer pump wavelengths in agreement with theoretical models.