title: Trace species detection in the near infrared using Fourier transform broadband cavity enhanced absorption spectroscopy: initial studies on potential breath analytes.
abstract: Cavity enhanced absorption measurements have been made of several species that absorb light between 1.5 and 1.7 µm using both a supercontinuum source and superluminescent light emitting diodes. A system based upon an optical enhancement cavity of relatively high finesse, consisting of mirrors of reflectivity ∼99.98%, and a Fourier transform spectrometer, is demonstrated. Spectra are recorded of isoprene, butadiene, acetone and methane, highlighting problems with spectral interference and unambiguous concentration determinations. Initial results are presented of acetone within a breath-like matrix indicating ppm precision at <∼10 ppm acetone levels. Instrument sensitivities are sufficiently enhanced to enable the detection of atmospheric levels of methane. Higher detection sensitivities are achieved using the supercontinuum source, with a minimum detectable absorption coefficient of ∼4 × 10(-9) cm(-1) reported within a 4 min acquisition time. Finally, two superluminescent light emitting diodes are coupled together to increase the wavelength coverage, and measurements are made simultaneously on acetylene, CO(2), and butadiene. The absorption cross-sections for acetone and isoprene have been measured with an instrumental resolution of 4 cm(-1) and are found to be 1.3 ± 0.1 × 10(-21) cm(2) at a wavelength of 1671.9 nm and 3.6 ± 0.2 × 10(-21) cm(2) at 1624.7 nm, respectively.
authors.affiliation: Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, UK.
authors.forename: W
authors.initials: W
authors.lastname: Denzer
authors.forename: G
authors.initials: G
authors.lastname: Hancock
authors.forename: M
authors.initials: M
authors.lastname: Islam
authors.forename: C E
authors.initials: CE
authors.lastname: Langley
authors.forename: R
authors.initials: R
authors.lastname: Peverall
authors.forename: G A D
authors.initials: GA
authors.lastname: Ritchie
authors.forename: D
authors.initials: D
authors.lastname: Taylor
mesh_terms: D000042:Absorption; D001944:Breath Tests / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D007259:Infrared Rays; D017550:Spectroscopy, Fourier Transform Infrared / Q000295:instrumentation / Q000379:methods*