Design of fibre laser and sensor systems for gas spectroscopy in the near-IR

Because of the ready availability of fibre optic components from the communications industry, fibre optic systems operating in the near-IR are well suited for remote, multi-point monitoring of hazardous and environmentally-important gases. However a number of challenges have to be met in order exploit the potential commercial opportunities and applications for such sensors. Here we review our research on gas sensors based on fibre laser systems and absorption spectroscopy. Fibre lasers are of particular interest for sensors since on-going developments have extended their wavelength range of operation over similar to1480-1620nm, encompassing the near-IR absorption lines of numerous gases. We discuss several configurations for fibre laser systems which offer the prospect of either enhanced performance or the possibility of multiplexing a number of sensor cells. However, because gas absorption lines in the near-IR spectral region are relatively weak, high sensitivity techniques are required for a number of species and we discuss methods for path-length enhancement through ring-down and intra-cavity absorption spectroscopy. Effective interrogation methods are required to attain the benefits of the various forms of cavity-enhanced spectroscopy in fibre optic systems and several techniques are under investigation to realise this potential.