0.5 kW of instantaneous power efficient lasing at 0.82 µm from all-fiber Tm3+-doped silica-based fiber laser

A high-power laser at 0.82 µm has been demonstrated using an 18-m-long thulium-doped silica-based fiber. This was cladding-pumped quasi-continuous-wave with up to 447 W of instantaneous power at 0.79 µm from pigtailed diode lasers. The thulium-doped fiber (TDF) was fabricated in-house, featuring a locally modified environment for thulium ions through co-doping with high concentrations of aluminum and lanthanum (La³⁺). This modification extended the fluorescence lifetime of the 3H4 level to approximately 50-µs for long-living ions, markedly longer than the ~14-µs typical for standard silica TDFs. An all-fiber laser cavity was formed by perpendicular cleaves at both fiber ends. Co-lasing at ~1.9 µm counteracted population-trapping in the 3F4 level. The instantaneous output power from both ends combined reached ~452 W in 250-µs pulses. The slope efficiency relative to absorbed pump power reached approximately 57.3%, with no observed power roll-off. The measured beam quality M2 at ~250 W output power were 2.2 and 2.45 in the orthogonal directions. To the best of our knowledge, this is the first reported demonstration of a high-power laser on the 3H4 → 3H6 transition in a cladding-pumped Tm-doped silica-based fiber laser.