Spectroscopic characterization and mode-locked pulse generation in Tm,Ho-codoped mixed sesquioxide crystal

We demonstrate, for the first time to the best of our knowledge, continuous-wave (CW) and mode-locked laser operation of a Tm³⁺,Ho³⁺-codoped mixed sesquioxide crystal at ∼2.1 µm. The spectroscopic properties of the Tm,Ho:YScO₃ crystal were systematically investigated. The crystal exhibits a peak absorption coefficient of 2.50 cm^-1 at 794 nm, corresponding to an absorption cross section of 2.78 × 10^-20 cm², with an absorption bandwidth (full width at half maximum, FWHM) of 17.3 nm. Furthermore, the CW laser generated 0.88 W pumped by a 1700-nm Raman fiber laser, with a slope efficiency of 44.7%, and exhibited a broad CW tuning range of 197.9 nm. Remarkably, the laser delivers soliton pulses as short as 151 fs at 2112.9 nm with an average output power of 328 mW and a pulse repetition rate of ∼85.6 MHz via semiconductor saturable absorber mirror (SESAM) mode-locking.