Watt-level CW 2.1µm laser based on Tm, Ho:GGAG crystal under in-band diode pumping at 1.7µm

A solid-state laser based on a Tm³⁺ and Ho³⁺ co-doped disordered garnet Tm, Ho:GGAG was investigated under resonant diode pumping in the 1.7μm spectral region. Compared to the standard pumping scheme at 0.8μm, this approach significantly reduces the quantum defect, relaxes restrictions on Tm³⁺ doping levels, and potentially broadens the gain spectrum in the 2.0 to 2.1μm range. The use of recently developed high-power diode lasers in this pump scheme remains largely unexplored in the literature. The benefits are further enhanced by employing a disordered garnet host which induces spectral line broadening. A hemispherical cavity was constructed and various output couplers with reflectivity from 80% to 99.7% were tested in a quasi-continuous (QCW) regime. Continuous-wave (CW) laser operation was demonstrated with the best performing OC and an output power of 2.8W was achieved with a slope efficiency of 41 ± 5% with respect to the absorbed power, and a threshold absorbed power of 0.6 W. Wavelength tuning using a birefringent filter was investigated under various conditions. The broadest recorded tuning range was 1933 to 2111nm under QCW pumping using a SiO₂ filter. CW tunability of 2011 to 2105nm with the power of 600mW at 2099nm was obtained using an MgF₂ filter. These results demonstrate that resonant diode pumping of Tm, Ho co-doped lasers combined with suitable host materials is a promising way to increase efficiency, power scalability and compactness of 2.1μm laser sources.