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.

High-efficiency ∼2 µm CW laser operation of LD-pumped Tm3+:CaF2 single-crystal fibers.

The Tm:CaF2 single-crystal fibers were successfully grown by modified temperature gradient technique method. The J-O intensity parameters, spontaneous radiative transition rates, radiative lifetimes and fluorescence branching ratios of Tm3+ were calculated with Judd-Ofelt theory. A systematic study of the fluorescence characteristics has been carried out. Simulated emission cross-sections of the 3F4 → 3H6 transition were calculated to be 6.68×10-21 cm-2 and 4.65×10-21cm-2 for crystal doped with 3 at.% and 4 at.% Tm3+. The 64.4% slope efficiency with output power of 2.23W was achieved in 3 at.% Tm:CaF2 single-crystal fiber. The slope efficiency decreased to 44.5% and maximum output power decreased to 1.65W in 4 at.% Tm:CaF2 single-crystal fiber. Obtained results show that Tm-doped CaF2 single-crystal fibers are promising materials for IR laser action generation.