Broadly tunable diode-pumped 2.1µm laser based on µ-PD grown Tm,Ho:GSAG

Miniature diode-pumped solid-state lasers operating in the 2.1µm atmospheric window are crucial for spectroscopic applications and free-space optical communication. We report on the spectroscopic and laser properties of a new Tm,Ho-codoped gadolinium-scandium-aluminium garnet (Tm,Ho:GSAG), a promising alternative to conventional hosts like YLF, YAG, and YAP. The mixed-garnet structure enables broad absorption and emission while maintaining the favorable thermo-mechanical properties of oxides. A Tm,Ho:GSAG crystal was grown by the µ-PD method, yielding a 3mm diameter, 20mm long rod. This technique enables the rapid and cost-effective preparation of small yet sufficiently high-quality laser-grade samples, facilitating extensive testing of different material compositions. A 3mm long sample with polished facets was prepared for laser testing. Spectroscopic characterization included absorption and emission spectra as well as fluorescence decay time measurements at 2.1µm. Laser experiments were conducted with a 782nm pulsed diode pump. In an untuned resonator, the laser achieved a slope efficiency of 25% with respect to absorbed pump power, with a peak emission at 2094nm. Wavelength tuning was implemented using an MgF₂ birefringent filter, covering a range from 2025nm to 2134nm, with maximum output power at 2122nm. These results demonstrate that Tm,Ho:GSAG is a promising gain medium for tunable diode-pumped mid-IR laser sources.