title: Open multipass absorption cell for in situ monitoring of stratospheric trace gas with telecommunication laser diodes.
abstract: A two-mirror multipass absorption cell that is operated open to the atmosphere from a stratospheric balloon to monitor in situ methane (in the 1.65-microm region) and water vapor (in the 1.39-microm region) with telecommunication laser diodes is described. A small Cassegrain-type telescope is used to couple the cell simultaneously with two near-infrared InGaAsP laser diodes by means of optical fibers. The 1-m cell provides an absorption path length of 56 m. The optical cell was carefully designed to be free of incidental fringing in the 10(-5) absorption range. It is used in combination with a dual-beam detector to obtain a detection limit of 10(-5) absorption units, a large dynamic range of the measurements of many orders of magnitude, and a precision error in the concentration determination of a few percents. The optical arrangement of the cell and its ability to be used to detect in situ trace gas in the stratosphere, in severe environmental conditions, are exposed.
authors.affiliation: Institut Pierre-Simon-Laplace, Service d'Aeronomie, Centre National de la Recherche Scientifique, Verrièresle-Buisson, France. georges.durry@aerov.jussieu.fr
authors.forename: Georges
authors.initials: G
authors.lastname: Durry
authors.forename: Théodore
authors.initials: T
authors.lastname: Danguy
authors.forename: Ivan
authors.initials: I
authors.lastname: Pouchet