Spectroscopy and 2.1 µm laser operation of Czochralski-grown Tm³⁺:YScO₃ crystals

We report on growth, temperature-dependent spectroscopy, and laser experiments of Tm³⁺-doped YScO₃ mixed sesquioxide crystals. For the first time, cm³-scale laser quality Tm³⁺:YScO₃ crystals with 2.2 at.% and 3.1 at.% doping levels were grown by the Czochralski method from iridium crucibles. We reveal that the structural disorder in the mixed crystals allows for broad and smooth spectral features even at cryogenic temperatures. We obtained the first continuous wave laser operation in this material at wavelengths around 2100 nm using a laser diode emitting at 780 nm as a pump source. A maximum slope efficiency of 45% was achieved using a Tm^3 +(3.1 at.%):YScO₃ crystal. Our findings demonstrate the high potential of Tm³⁺-doped mixed sesquioxides for efficient ultrafast pulse generation in the 2.1 µm range.