Thulium fiber pumped tunable Ho:CaF₂ laser

The paper reports the first room-temperature operation of the in-band pumped Ho:CaF₂ laser. A set of Ho:CaF₂ crystals varying in holmium concentrations (from 0.1 up to 2.5 mol. % of HoF₂), synthesized using the Bridgeman technique, was used for lasing and related spectroscopy investigation. A pulsed 1.94 μm thulium fiber laser system was used for Ho:CaF₂ longitudinal pumping. For 1.5 mol. % of Ho:CaF₂, the maximal wavelength tunability (from 2073 to 2114 nm) and output energy (1.6 mJ at 2113 nm) were obtained for absorbed pumping energy 34 mJ. Without the tuning element, the slope efficiency up to 30% in respect to absorbed power was obtained using this sample.