title: Remote open-path cavity-ringdown spectroscopic sensing of trace gases in air, based on distributed passive sensors linked by km-long optical fibers.
abstract: A continuous-wave, rapidly swept cavity-ringdown spectroscopic technique has been developed for localized atmospheric sensing of trace gases at remote sites. It uses one or more passive open-path optical sensor units, coupled by optical fiber over distances of >1 km to a single transmitter/receiver console incorporating a photodetector and a swept-frequency diode laser tuned to molecule-specific near-infrared wavelengths. Ways to avoid interference from stimulated Brillouin scattering in long optical fibers have been devised. This rugged open-path system, deployable in agricultural, industrial, and natural atmospheric environments, is used to monitor ammonia in air. A noise-limited minimum detectable mixing ratio of ~11 ppbv is attained for ammonia in nitrogen at atmospheric pressure.
authors.forename: Yabai
authors.initials: Y
authors.lastname: He
authors.forename: Chunjiang
authors.initials: C
authors.lastname: Jin
authors.forename: Ruifeng
authors.initials: R
authors.lastname: Kan
authors.forename: Jianguo
authors.initials: J
authors.lastname: Liu
authors.forename: Wenqing
authors.initials: W
authors.lastname: Liu
authors.forename: Julian
authors.initials: J
authors.lastname: Hill
authors.forename: Ian M
authors.initials: IM
authors.lastname: Jamie
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Orr