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Proceedings Paper

Wavelength modulation spectroscopy with a pulsed quantum cascade laser
Author(s): Jagadeeshwari Manne; Alan Lim; Wolfgang Jäger; John Tulip
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Paper Abstract

A pulsed distributed feedback quantum cascade laser (QCL) operating near 957 cm-1 was employed in wavelength modulation mode for spectroscopic trace gas sensing applications. The laser was excited with short current pulses (5-10 ns) with < 2% duty cycle. The pulse amplitude was modulated with a linear sub-threshold current ramp at 20 Hz resulting in a ~ 2.5 cm-1 frequency scan, which is typically wider than what has been reported for these lasers, and would allow one to detect molecular absorption features with line widths up to 1 cm-1. A demodulation approach followed by numerical filtering was utilized to improve the signal-to-noise ratio. We then superimposed a sine wave current modulation at 10 kHz onto the 20 Hz current ramp. The resulting high frequency temperature modulation of the distributed feedback (DFB) structure results in wavelength modulation (WM). The set-up was tested by recording relatively weak absorption lines of carbon dioxide. We demonstrated a minimum detectable absorbance of 10-5 for this spectrometer. Basic instrument performance and optimization of the experimental parameters for sensitivity improvement are discussed.

Paper Details

Date Published: 23 August 2011
PDF: 7 pages
Proc. SPIE 8173, Photonics 2010: Tenth International Conference on Fiber Optics and Photonics, 81730D (23 August 2011); doi: 10.1117/12.900116
Show Author Affiliations
Jagadeeshwari Manne, Univ. of Alberta (Canada)
Alan Lim, Univ. of Alberta (Canada)
Wolfgang Jäger, Univ. of Alberta (Canada)
John Tulip, Univ. of Alberta (Canada)

Published in SPIE Proceedings Vol. 8173:
Photonics 2010: Tenth International Conference on Fiber Optics and Photonics
Sunil K. Khijwania; Banshi D. Gupta; Bishnu P. Pal; Anurag Sharma, Editor(s)

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