The structure and operation principle of the infrared (3.39 μm) laser methanometer have been presented. Fluoride glass optical cables are used in the instrument. Methane detection characteristics of the 3.39 μm absorption line as compared to those at 1.67μm and 1.33μm in the overtone range have been discussed. The dual wavelength (3.39/0.63μm) laser/fibre-optic methane measuring system for measuring emission from extended methane generators has been presented and the related phenomena, such as mutual extinction and refraction of both versions of equipment, in particular to coal mining and environmental monitoring have been discussed.
"Mid-infrared laser/fibre-optic methanometer", Proc. SPIE 4185, Fourteenth International Conference on Optical Fiber Sensors, 418549 (9 November 2000); doi: 10.1117/12.2302296; https://doi.org/10.1117/12.2302296