High-brightness and tunable lasers operating in the 1800-2000 nm wavelength region are very attractive for applications such as spectroscopy, atmospheric remote sensing and medical surgery. So far, Tm3+-doped crystalline hosts, such as YLF and YAG, have proven to be ones of the most interesting gain materials [1, 2]. Among other available hosts, Tm:CaF2 offers a high thermal conductivity and a very broad emission bands due to multisite crystal structure. Therefore, Tm:CaF2 is a good candidate for high-power and broadband tunable laser emission between 1750 nm and 2000 nm. However, there are only a few reports on Tm:CaF2 laser operation, mainly because of the lack of powerful pump sources at the optimum absorption wavelength of 767 nm, when using cross-relaxation process . In comparison, in-band pumping of Tm-doped materials can be very efficient as the quantum defect may approach 85% [4, 5].
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