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Remote laser analyzer for methane sensing in the air of subterranean spaces

The paper concerns with calculative and experimental development of a remote electric-discharge DF-laser analyzer for subterranean methane monitoring up to its explosive concentrations. The analyzer is built according to lidar scheme when the probing emission is reflected by artificial or natural objects located on a subterranean measurement path. Methane records in the air are made using the differential absorption technique. The required metrological parameters of the analyzer are reached with the multi- frequency laser atmospheric control. The experimental factors of methane absorption in a spectral range from 3.6 to 3.8 micrometers and DF laser energy performance per line in a spectral range from 3.5 to 4.0 micrometers generated with a tunable selective resonator are performed. An excess of a factor 2 to 30 per the per line probing energy of the lidar operating with selective resonator over that with non- selective one is demonstrated. The probing energy of the lidar operating with selective resonator over that with non- selective one is demonstrated. The performed theoretical calculations determine the required power of providing radiation, optical on/off - line combinations of the laser, and measurement accuracy attained on measurement paths from 10 to 100 m long with the allowance for measurement- interfering factors under the conditions of detection of diffusively reflected lidar return form artificial and natural objects. A block diagram of the methane analyzer is given and procedures for multi-frequency probing of the mine medium are performed for a spectral range from 3.6 to 3.8 micrometers .