Highly-efficient Resonantly Diode-pumped 2 µm Thulium Lasers

Tm-based lasers are direct sources of high-power radiation in 2- µm spectral region ( 3 F 4 → 3 H 6 transition of Tm 3+ ) with applications in medicine, high-resolution spectroscopy, and remote sensing. The long storage time of 3 F 4 upper laser level and efficient energy extraction could help to build high-energy, high-mean-power laser systems in the near future. [1] Efficient high-power 2 µm lasing, based on 0.8 µm laser diode (LD) pumping at 3 H 6 → 3 H 4 transition, was previously attained in Tm-doped hosts such as YAG, LuAG, YLF, YAP, and GdVO 4 . [2] , [3] The resonant Tm 3+ excitation directly to the 3 F 4 is now possible thanks to commercially available high power ( > 30 W) LD operating at 1.7 µm spectral range. There are several benefits of this pumping scheme: even lower quantum defect of the pumping process ( < 15 %); significantly broader absorption lines of 3 H 6 → 3 F 4 transition of Tm 3+ comparing to 3 H 6 → 3 H 4 transition; eye-safety of pumping radiation. The goal of this work was an investigation of well-established crystalline Tm-laser materials Tm:YAG, Tm:YAP, and Tm:YLF operating at 2 µm laser transition under longitudinal 1.7 µm resonant LD pumping.