Remote Detection of Gases by Diode Laser Spectroscopy

Abstract A new method is demonstrated for the remote optical detection of gases based on the differential absorption of radiation from two longitudinal modes of a laser diode. The sensor is shown to be capable of measuring 2000 p.p.m. of methane in air using a 1 m optical path length and a 2·5 km optical fibre link. A stability of better than 1 Torr of methane over a period of 10 h has been demonstrated.