Excitation scheme for the upper energy levels in a Tm:Yb:BaY_2F_8 laser crystal

Energy-transfer processes (including upconversion) are quantitatively studied in a Tm:Yb:BaY2F8 laser crystal. Several energy-transfer, cross-relaxation, and upconversion parameters are determined. We prove that at excitation of the crystal via Yb ions, the Tm levels 3F4, 3H4, 3F3,2, 1G4, and 3P0 are populated via Yb–Tm interaction, and the level 1D2 is likely populated owing to 3F3 Tm–3F3 Tm upconversion. The possibility of resonant excited-state absorption at 706 nm and resonant energy-transfer upconversion populating the level 1D2 are discussed. The possibility of avalanche pumping of Tm:Yb:BaY2F8 at 706 nm is shown.