Ultra-efficient Er:YAG laser with 60W output power at 1645nm end-pumped by an Er-Yb co-doped fibre laser

High-power solid-state lasers operating in the eyesafe wavelength regime around ~1.5-1.6 µm have numerous applications and provide an ideal platform for nonlinear frequency conversion to the mid-infrared. The traditional approach for producing laser output in this wavelength region is via direct diode pumping of erbium-ytterbium codoped bulk glass or crystal lasers. Power scaling of such lasers has proved rather difficult due to the high thermal loading density which results from a large quantum defect, the need for a relatively high active ion concentrations and additional heat loading due to energy-transfer-upconversion. Another approach for generating laser emission in the 1.5-1.6 µm wavelength regime is via cladding-pumping of erbium-ytterbium co-doped fibre lasers. Fibre lasers are becoming increasingly attractive for high power generation due to their high efficiency and immunity from thermal effects. However, due to their small core sizes and long device length, fibre laser suffer from detrimental nonlinear effects and are susceptible to core damage, especially when operating in the high peak power pulsed regime. In-band pumping of bulk solid-state lasers with high-brightness fibre sources is an attractive alternative approach which combines the advantages of efficient cw high-power generation in cladding-pumped fibre lasers with the energy storage and high pulse energy capabilities of bulk solid-state laser crystals. A key attraction of this fibre-bulk hybrid laser scheme is that most of the heat generated via quantum defect heating is deposited in the fibre, and thermal effects in the bulk laser are dramatically reduced leading to the prospect of much improved efficiency, beam quality and higher average output power. This approach has already been successfully applied to Er:YAG [1] and Er:LuAG [2] lasers pumped (in-band) by an erbium fibre laser, with multi-watt average powers up to ~7W and slope efficiencies with respect to incident pump power up to 54% and 40% respectively. In this paper we report an Er:YAG laser with much higher output power and higher efficiency end-pumped by a tunable cladding-pumped Er,Yb fibre laser. The laser yielded 60 W of output at 1645.3 nm for 82 W of incident pump power from the Er,Yb fibre laser at 1532 nm. The corresponding slope efficiency was 80.7% with respect to incident pump power