Spectroscopic characterization and efficient tunable lasers of Ho:BaF2 single crystals

A high-quality 1% (atom fraction) Ho 3+ :BaF 2 crystal was successfully grown using the temperature gradient technique (TGT).The optical properties of the crystal were investigated, and continuous-wave (CW) laser operation of Ho 3+ ions in the 2 m range was successfully demonstrated for the first time in the BaF 2 crystal, to the best of our knowledge.Spectral parameters such as t (t = 2, 4, 6) and radiative lifetimes were calculated and studied by the Judd-Ofelt (J-O) theory.The quality factor was calculated to be Q = 6.60 10 -20 cm 2 ms, and the full width at half-maximum (FWHM) was fitted to be 134.5 nm, indicating that the Ho:BaF 2 crystal has a low laser threshold and broadband tunability.A maximum output power of 1.5 W and a slope efficiency of 29.3% were achieved by the 1908 nm fiber laser as the pumping source, with a relatively low threshold of 399 mW.Additionally, the Ho:BaF 2 crystal achieved a tunable laser output with a bandwidth of 166.4 nm, which is the widest as reported for other 2 m band Ho-doped fluoride crystals to the best of our knowledge.These results suggest that the Ho: BaF 2 crystal has the potential to achieve femtosecond ultrafast pulse laser output through mode-locking operation.