Highly sensitive detection of trace gases using the time-resolved frequency downchirp from pulsed quantum-cascade lasers

Michael T. McCulloch, Erwan L. Normand, Nigel Langford, Geoffrey Duxbury, D.A. Newnham

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A spectrometer using a pulsed, 10.25-µm-wavelength, thermoelectrically cooled quantum-cascade distributed-feedback laser has been developed for sensitive high-resolution infrared absorption spectroscopy. This spectrometer is based upon the use of the almost linear frequency downchirp of up to 75 GHz produced by a square current drive pulse. The behavior of this downchirp has been investigated in detail using high-resolution Fourier-transform spectrometers. The downchirp spectrometer provides a real-time display of the spectral fingerprint of molecular gases over a wave-number range of up to 2.5 cm^-1. Using an astigmatic Herriott cell with a maximum path length of 101 m and a 5-kHz pulse repetition rate with 12-s averaging, absorption lines having an absorbance of less than 0.01 (an absorption of less than 1%) may be measured.
Original languageEnglish
Pages (from-to)1761-1768
Number of pages7
JournalJournal of the Optical Society of America B
Issue number8
Publication statusPublished - Aug 2003


  • spectrometer
  • quantum physics
  • lasers
  • infrared absorption spectroscopy
  • optics

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