Excited-state absorption and upconversion pumping of Tm<sup>3+</sup>-doped potassium lutetium double tungstate
Aleksey Tyazhev, Pavel Loiko, Lauren Guillemot, Alexandre Kouta, Rosa Maria Solé, Xavier Mateos, Magdalena Aguiló, Francesc Dı́az, Hippolyte Dupont, Patrick Georges, Frédéric Druon, Alain Braud, Patrice Camy, Ammar Hideur
Abstract
We report on a bulk thulium laser operating on the 3 H 4 → 3 H 5 transition with pure upconversion pumping at 1064 nm by an ytterbium fiber laser (addressing the 3 F 4 → 3 F 2,3 excited-state absorption (ESA) transition of Tm 3+ ions) generating 433 mW at 2291 nm with a slope efficiency of 7.4% / 33.2% vs. the incident / absorbed pump power, respectively, and linear laser polarization representing the highest output power ever extracted from any bulk 2.3 µm thulium laser with upconversion pumping. As a gain material, a Tm 3+ -doped potassium lutetium double tungstate crystal is employed. The polarized ESA spectra of this material in the near-infrared are measured by the pump-probe method. The possible benefits of dual-wavelength pumping at 0.79 and 1.06 µm are also explored, indicating a positive effect of co-pumping at 0.79 µm on reducing the threshold pump power for upconversion pumping.