Laser-diode-pumped Tm:SrF₂ single crystal for high efficiency CW laser operation at ∼2 µm

A Tm:SrF₂ single crystal is grown by a modified temperature gradient technique (TGT). A study of the fluorescence characteristics and laser performance is carried out. Under laser-diode (LD) end-pumping, a continuous-wave (CW) laser is demonstrated. A slope efficiency of up to 81.8% is first achieved in the Tm-doped single crystals, which is extremely close to the photon quantum efficiency of 2.00. Such a high photon quantum efficiency is caused by the effective cross-relaxation process between Tm³⁺ ions. A maximum output power of 4.082 W is also obtained. The laser performance indicates that Tm:SrF₂ is a promising candidate for highly efficient ∼2 µm lasers.