Efficient room temperature continuous wave laser operation of Tm:YLF around 820 nm

We report on room-temperature continuous wave laser operation on the ³H₄→³H₆ transition in Tm³⁺(1 at.%):LiYF₄ (YLF). Under Ti:sapphire pumping at 781 nm, we achieved a maximum output power of 865 mW at a wavelength of 820 nm with a slope efficiency of 54%. Laser operation was demonstrated at 813, 815, 822, and 834 nm. Our spectroscopic analysis reveals spectrally broad and smooth gain spectra beneficial for wavelength tuning and short pulse generation but shows that a significant fraction of the population is trapped in the metastable ³F₄ level.