摘要： 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 [3]. In comparison, in-band pumping of Tm-doped materials can be very efficient as the quantum defect may approach 85% [4, 5]. In this contribution, we demonstrate the tunable laser emission of Tm:CaF2 crystal at 1775-1955 nm using in-band pumping by a fiber laser system at 1610 nm. We employed a linear plane-concave resonator built around a Tm:CaF2 crystal doped at 3% and 5 mm long (Fig. 1). The plane input mirror (M1) has transmission of 98% at the pump wavelength and is HR near 1850 nm, the concave output mirror (M2) has a transmission of 5-10% at 1850 nm. A birefringent plate can be inserted into the cavity at Brewster angle to act as a wavelength selective component. The pump source used in the experiments is an all-fiber MOPA specifically designed for an emission wavelength at 1610 nm. The MOPA consists of a 12 mW seed laser diode amplified into a two-stage fiber amplifier. A 50 nm band-pass filter centered at 1620 nm was used to suppress the ASE at 1530-1560 nm from the pre-amplifier stage. The power-amplifier stage is based on a 10 m long Er/Yb-codoped double-clad fiber pumped at 915 nm in order to maximize the gain on the long wavelength side. The 1610 nm MOPA laser source achieves more than 2.5 W of diffraction-limited power incident on the crystal, with a 0.5 nm spectral linewidth. Using a 10% transmission output coupler and without the birefringent plate, a maximum output power of 1.25 W is obtained, which represents a conversion efficiency of 70% with respect to the absorbed pump power. Inside the resonator, the pump beam waist is measured to be 45 μm and the signal beam waist is about 60 μm. As shown in Fig. 2, using an intra-cavity birefringent plate and a T2=5% output coupler, it was possible to tune the laser over 180 nm. Compared to a previous report [3], shorter wavelengths below 1800 nm are achieved thanks to the high-brightness pump source at 1610 nm. At the highest output power, the laser beam quality factors M2 of the laser is measured to be 1.1. These results are promising for the future development of in-band pumped mode-locked Tm:CaF2 laser.