High power in-band pumped Er:YAG laser at 1617 nm

摘要

Laser sources operating in the eye-safe wavelength regime around 1.5-1.6 μm have applications in a number of areas including, remote sensing, ranging and free-space communications. For many of these applications, the requirement for high output power is often supplemented by the need for high efficiency and good beam quality. This combination of operating characteristics is very difficult to achieve in conventional diode-pumped solid-state lasers based on erbium doped crystals (sensitised with Yb) owing to the relatively high fractional heat loading which results from the large quantum defect (～ 40%) and energy-transfer-upconversion. To alleviate this problem, attention has recently turned to singly-doped crystals (e.g. Er:YAG) and in-band pumping using an Er,Yb fibre laser. This approach has the advantage that most of the waste heat is generated in the fibre, which is largely immune to thermal effects, and quantum defect heating in the Er-doped crystal is very small (～7%). Using this hybrid laser scheme, we have demonstrated ～60 W of continuous-wave output from an Er:YAG laser at 1645 nm with a slope efficiency of 80%. However, for some remote sensing applications this operating wavelength is a little inconvenient, since there are atmospheric absorption lines due to methane which are in very close proximity necessitating careful selection and control of the lasing wavelength. Er:YAG also has a transition from the same upper level manifold (4{sup left}I{sub}(13/2)) at 1617 nm, which lies in a region of the spectrum where there are no atmospheric absorption lies. However, this transition has a much more pronounced three-level character and hence a much higher threshold pump power, so it has received little attention in spite of its obvious advantages for certain applications. Here, we report preliminary results for power scaling of an Er:YAG laser at 1617 nm in-band pumped by a high-power cladding-pumped Er,Yb fibre laser.