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Applied Optics

Applied Optics

APPLICATIONS-CENTERED RESEARCH IN OPTICS

  • Editor: Joseph N. Mait
  • Vol. 50, Iss. 25 — Sep. 1, 2011
  • pp: E112–E118

Wavelength modulation spectroscopy with a pulsed quantum cascade laser for the sensitive detection of acrylonitrile

Jagadeeshwari Manne, Alan Lim, Wolfgang Jäger, and John Tulip  »View Author Affiliations


Applied Optics, Vol. 50, Issue 25, pp. E112-E118 (2011)
http://dx.doi.org/10.1364/AO.50.00E112


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Abstract

A pulsed, distributed feedback (DFB) quantum cascade laser centered at 957 cm 1 was used in combination with a wavelength modulation spectroscopic technique for the detection of acrylonitrile. The laser was excited with short current pulses ( 5 10 ns ), and the pulse amplitude was modulated with a linear subthreshold current ramp at 20 Hz resulting in a 2.5 cm 1 frequency scan. This allowed the measurement of spectroscopic features of acrylonitrile with absorption line widths of 1 cm 1 . A demodulation approach followed by numerical filtering was utilized to improve the signal-to-noise ratio. We then superimposed a 10 kHz sine wave current modulation on top of the 20 Hz current ramp. The resulting high frequency temperature modulation of the DFB structure results in wavelength modulation. A minimum detectable absorbance of 10 5 , corresponding to the sub 10 9 levels of acrylonitrile, was achieved with less than a minute averaging time.

© 2011 Optical Society of America

OCIS Codes
(280.3420) Remote sensing and sensors : Laser sensors
(300.1030) Spectroscopy : Absorption
(300.6340) Spectroscopy : Spectroscopy, infrared
(300.6380) Spectroscopy : Spectroscopy, modulation
(140.5965) Lasers and laser optics : Semiconductor lasers, quantum cascade

History
Original Manuscript: June 2, 2011
Manuscript Accepted: July 8, 2011
Published: August 8, 2011

Citation
Jagadeeshwari Manne, Alan Lim, Wolfgang Jäger, and John Tulip, "Wavelength modulation spectroscopy with a pulsed quantum cascade laser for the sensitive detection of acrylonitrile," Appl. Opt. 50, E112-E118 (2011)
http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-50-25-E112

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