Extremely high sensitivity gas detection at 2.3 μm using a grazing incidence Tm3+ fibre laser cavity

Abstract Tm3+, when doped into fluoride fibre produces a broad emission centred around wavelength, λ=2.3 μm in the near infra-red. When placed within a laser cavity and pumped at λ=790 nm, tunable laser action is observed. Using a grazing incidence laser cavity arrangement, a wavelength tuning range Δλ=130 nm was achieved along with a very narrow emission linewidth Δν=207 MHz. We have used this laser as part of a gas sensing arrangement and have demonstrated an extremely high gas detection sensitivity of better than 50 ppm m using CH4 as a representative hydrocarbon gas. This system has the potential for use as part of a high sensitivity gas detection system for hydrocarbons and also for CO and HF which exhibit optical absorption in the spectral region around λ=2.3 μm.