title: Pulsed indirect photoacoustic spectroscopy: application to remote detection of condensed phases.
abstract: The technique of pulsed indirect photoacoustic spectroscopy is applied to the examination of free liquid surfaces, and the prospects are assessed for remote detection and identification of chemical species in a field environment. A CO(2) laser (tunable within the 9-11-microm region) provides pulsed excitation for a variety of sample types; the resulting photoacoustic pulses are detected at ranges of the order of a few centimeters. The phenomenon is investigated as a function of parameters such as temperature, sample depth, laser-pulse energy, pulse length, and beam diameter. The results are in good agreement with a theoretical model that assumes the mechanism to be expansion of air resulting from heat conduction from the laser-heated surface of the sample under investigation. Signal and noise processing issues are discussed briefly, and the possible extension of the technique to ranges of the order of 10 m is assessed.
authors.affiliation: Electronics Sector, Defence Evaluation and Research Agency, Malvern, Worcestershire WR14 3PS, UK. mharris@dera.gov.uk
authors.forename: M
authors.initials: M
authors.lastname: Harris
authors.forename: G N
authors.initials: GN
authors.lastname: Pearson
authors.forename: D V
authors.initials: DV
authors.lastname: Willetts
authors.forename: K
authors.initials: K
authors.lastname: Ridley
authors.forename: P R
authors.initials: PR
authors.lastname: Tapster
authors.forename: B
authors.initials: B
authors.lastname: Perrett