Tunable and efficient diode-pumped Tm3+-doped fluoride fiber laser for hydrocarbon gas sensing

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Abstract
The operation of an efficient diode laser pumped continuous wave thulium-doped fiber laser emitting at wavelength λ = 2.31 μm is reported. The operation of the fiber laser is optimized with a view to producing a small and efficient laser source for optical absorption-based gas sensing. A 2-mW output power combined with a high slope efficiency make this fiber laser a useful source for sensing spectroscopic-based hydrocarbon gases that absorb around λ = 2.3 μm. A lower limit of detection of 1000 ppm. meters for methane is routinely demonstrated using an unoptimized Fabry-Perot cavity laser system. The tunability of the fiber laser has also been investigated in order to target specific hydrocarbon absorption features. Initial results with a diffraction grating tuned system suggest detectivities of < 150 ppm.m may be obtained.