High-Efficiency 2.09 μm Single-Oscillator Monolithic Thulium-Doped Fiber Laser

A single-oscillator monolithic thulium-doped fiber laser in which the 793 nm core absorption of 8.42 dB/m allows emitting 193 W (46 % of slope efficiency) at
$2.09~\mu \text{m}$
is presented. An 8°-cleaved angle of the fiber facet suppresses the parasitic cavity that formerly limited the power scaling. The characteristics of the thulium laser operating at the uncommon 2.09-
$\mu \text{m}$
long wavelength is compared to the power performances of a similar thulium-holmium codoped fiber laser.