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Proceedings Paper

Multiplexed gas spectroscopy using tunable VCSELs
Author(s): Mihail Bora; James McCarrick; Jim Zumstein; Steven Bond; Allan Chang; Bryan Moran; William J. Benett; Tiziana Bond
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Paper Abstract

Detection and identification of gas species using tunable laser diode laser absorption spectroscopy has been performed using vertical cavity surface emitting lasers (VCSEL). Two detection methods are compared: direct absorbance and wavelength modulation spectroscopy (WMS). In the first, the output of a DC-based laser is directly monitored to detect for any quench at the targeted specie wavelength. In the latter, the emission wavelength of the laser is modulated by applying a sinusoidal component on the drive current of frequency ω, and measuring the harmonics component (2ω) of the photo-detected current. This method shows a better sensitivity measured as signal to noise ratio, and is less susceptible to interference effects such as scattering or fouling. Gas detection was initially performed at room temperature and atmospheric conditions using VCSELs of emission wavelength 763 nm for oxygen and 1392 nm for water, scanning over a range of approximately 10 nm, sufficient to cover 5-10 gas specific absorption lines that enable identification and quantization of gas composition. The amplitude and frequency modulation parameters were optimized for each detected gas species, by performing two dimensional sweeps for both tuning current and either amplitude or frequency, respectively. We found that the highest detected signal is observed for a wavelength modulation amplitude equal to the width of the gas absorbance lines, in good agreement with theoretical calculations, and for modulation frequencies below the time response of the lasers (<50KHz). In conclusion, we will discuss limit of detection studies and further implementation and packaging of VCSELs in diode arrays for continuous and simultaneous monitoring of multiple species in gaseous mixtures.

Paper Details

Date Published: 9 May 2012
PDF: 6 pages
Proc. SPIE 8366, Advanced Environmental, Chemical, and Biological Sensing Technologies IX, 836607 (9 May 2012); doi: 10.1117/12.920803
Show Author Affiliations
Mihail Bora, Lawrence Livermore National Lab. (United States)
James McCarrick, Lawrence Livermore National Lab. (United States)
Jim Zumstein, Lawrence Livermore National Lab. (United States)
Steven Bond, Lawrence Livermore National Lab. (United States)
Allan Chang, Lawrence Livermore National Lab. (United States)
Bryan Moran, Lawrence Livermore National Lab. (United States)
William J. Benett, Lawrence Livermore National Lab. (United States)
Tiziana Bond, Lawrence Livermore National Lab. (United States)


Published in SPIE Proceedings Vol. 8366:
Advanced Environmental, Chemical, and Biological Sensing Technologies IX
Tuan Vo-Dinh; Robert A. Lieberman; Günter Gauglitz, Editor(s)

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