Abstract

Mid-infrared photonics has attracted growing interest in recent years owing to the presence of many strong characteristic vibrational transitions that are highly resonant with the low-energy photons of the mid-infrared. As such, there are a wealth of potential applications that would benefit from the availability of well understood, robust sources in this wavelength range including spectroscopy and medicine [1]. Of particular interest is the region surrounding 3 μm which corresponds to the antisymmetric stretch of the OH bond in water coupled with a region of high atmospheric transmission. ZrF₄-BaF₂-LaF₃-AlF₃-NaF (ZBLAN) based fibre lasers operating on the ⁴I_11/2→⁴I_13/2 transition of Er³⁺ ion dopant are currently the most heavily researched in this region, delivering up to 24 W of output power at 2.8 μm [2]. Alternatively, Ho³⁺ doped ZBLAN systems allow for lasing of the ⁵I₆→⁵I₇ transition at 2.9 μm. Such systems remain particularly viable candidates for high powered operation as they offer a comparatively higher Stokes efficiency limit of 40.5 % (when pumped at 1150 nm) coupled with reduced pump excited state absorption. However, demonstrations of high powered emission have been limited by available pump power [3]. Preliminary results have suggested that this can be overcome through the use of an Yb³⁺-Raman fibre laser pump system which offers single mode, power scalable output at 1150 nm [4] and can be pumped using commercially available high-powered 976 nm diode lasers.

© 2015 IEEE