23 August 2011 Wavelength modulation spectroscopy with a pulsed quantum cascade laser
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Proceedings Volume 8173, Photonics 2010: Tenth International Conference on Fiber Optics and Photonics; 81730D (2011) https://doi.org/10.1117/12.900116
Event: International Conference on Fiber Optics and Photonics, 2010, Guwahati, India
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.
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Jagadeeshwari Manne, Alan Lim, Wolfgang Jäger, John Tulip, "Wavelength modulation spectroscopy with a pulsed quantum cascade laser", Proc. SPIE 8173, Photonics 2010: Tenth International Conference on Fiber Optics and Photonics, 81730D (23 August 2011); doi: 10.1117/12.900116; https://doi.org/10.1117/12.900116
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