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Applied Optics

Applied Optics


  • Editor: Joseph N. Mait
  • Vol. 49, Iss. 8 — Mar. 10, 2010
  • pp: 1406–1413

Enhancement of trace gas detection by integrating wavelength modulated spectra across multiple lines

Andreas Karpf and Gottipaty N. Rao  »View Author Affiliations

Applied Optics, Vol. 49, Issue 8, pp. 1406-1413 (2010)

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We describe and demonstrate a technique that enhances the sensitivity of a spectrometer for trace gas detection by employing wavelength modulation spectroscopy (WMS) and integrating the absolute value of the recorded spectra across multiple lines of the species. The sensitivity is further enhanced by conducting WMS with large modulation depths. This technique is demonstrated using a continuously tunable external cavity CW quantum cascade laser to record the second harmonic wavelength modulated spectra of NO 2 across the peak of the R-branch from 1629.5 to 1633.9 cm 1 . By integrating the absolute value of the resulting spectra, the detection sensitivity of NO 2 is improved by a factor of 40 compared to the sensitivity achieved using single-line WMS with the same apparatus. By using this technique, we achieve a sensitivity of approximately 6   parts   in   10 9 (ppb) using a short-path cell (a 1 m absorption cell with two passes).

© 2010 Optical Society of America

OCIS Codes
(000.2170) General : Equipment and techniques
(010.1120) Atmospheric and oceanic optics : Air pollution monitoring
(120.6200) Instrumentation, measurement, and metrology : Spectrometers and spectroscopic instrumentation
(280.3420) Remote sensing and sensors : Laser sensors
(300.6340) Spectroscopy : Spectroscopy, infrared

ToC Category:
Remote Sensing and Sensors

Original Manuscript: October 29, 2009
Revised Manuscript: January 27, 2010
Manuscript Accepted: February 5, 2010
Published: March 8, 2010

Andreas Karpf and Gottipaty N. Rao, "Enhancement of trace gas detection by integrating wavelength modulated spectra across multiple lines," Appl. Opt. 49, 1406-1413 (2010)

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