Multi-mode 2 m Tm-silica fibre lasers with 1.61 μm in-band pumping

In-band pumping of multi-mode Tm-silica fibre lasers operating at 2 m has strong potential due to higher quantum efficiency, increased damage threshold, increased nonlinear threshold and practical larger pumping area. Results are presented on the investigation of multi-mode Tm-silica fibre lasers operating near 1.85 m, containing a high Tm doping concentration of 1.1 wt% (9 1025 m-3), when in-band pumped at 1.61 m near an absorption peak in Tm-silica. The relationships between lasing performance and fibre length and cavity losses are reported. The measured highest slope efficiency and threshold achieved are about 42% and 0.4 W obtained with a short optimum fibre length of 23 cm and cavity reflectivities of (99%-4%), and on a small scale in this configuration a maximum output power of 370 mW was produced. The estimated maximum slope efficiency for the cavity reflectivities of (4%-4%) is up to 56%.