Investigation of Yb: LuAG crystals with high doping concentration

摘要

Two Yb:LuAG (Yb:Lu_3Al_5O_(12)) plates (thickness 1.05 mm, diameter 3 mm, AR/AR @ 0.9 - 1.1 μm, Yb-doping c = 15 % and 20 %) were prepared for laser experiments. For Yb:LuAG pumping, fibre coupled laser diode operating in pulsed regime was used (fibre core diameter 100μm, emission wavelength 968 nm, pulse length 2 ms, repetition rate 10 Hz, maximum energy 40 mJ). The longitudinally pumped Yb:LuAG was placed inside the 148 mm long resonator formed by a flat pumping mirror (HR @ 1.0 - 1.1 μm, HT @ 0.97 μm) and by a curved output coupler (radius of curvature 150 mm). Set of output couplers with reflectivity R = 70 - 97% @ 1.0 - 1.1 μm was used and the output power amplitude was measured in dependence on absorbed pumping power amplitude. It was found that for both samples the output coupler reflectivity had only minor influence on laser output parameters expect emission wavelength (1048 nm for R ＞ 90% and otherwise 1031 nm). The sample with lower concentration had a lower threshold (～ 2.5 W for c = 15% and ～ 3.0 W for c = 20%) and higher slope efficiency (～ 61% for c = 15% and ～ 50% for c = 20%). The maximum output power amplitude 6.7 W was obtained using Yb:LuAG with c = 20 % and R = 92 % for pumping power amplitude 14 W. Obtained results confirmed the good quality of newly grown highly doped YbrLuAG crystals.