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

Tm3+, when doped into fluoride fibre produces a broad emission centred around wavelength, lambda = 2.3 mum in the near infra-red. When placed within a laser cavity and pumped at lambda = 790 nm, tunable laser action is observed. Using a grazing incidence laser cavity arrangement. a wavelength tuning range Delta lambda = 130 nm was achieved along with a very narrow emission linewidth Delta nu = 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 lambda = 2.3 mum. (C) 2001 Elsevier Science B.V. All rights reserved.