Continuous-wave mid-infrared laser operation of Tm:KYF at 2.3 μm.

We report continuous-wave lasing demonstration of a Tm:KYF crystalline gain medium at 2343 nm. A narrow-linewidth, tunable, continuous-wave Ti:sapphire laser was used to end pump a Tm:KYF crystal with thulium doping of 8 at. %. With 1 W of pump power, the resonator with a 1% output coupler generated output powers of 31 and 122 mW in single-pumping and double-pumping configurations, respectively. Excitation efficiency of the laser was investigated for pump wavelengths in the 765-806 nm range. Four pump bands were identified in this wavelength range, with the two most efficient pump bands centered at 773 and 778 nm. The output of the laser could be tuned smoothly and continuously over a spectral width of 125 nm from 2260 to 2385 nm. The lifetime of the H3 level was further measured to be 16 μs, and the emission cross section was determined based on lasing threshold measurements.