Using a wavelength-modulated quantum cascade laser to measure NO concentrations in the parts-per-billion range for vehicle emissions certification

W. H. Weber, J. T. Remillard, R. E. Chase, J. F. Richert, F. Capasso, C. Gmachl, A. L. Hutchinson, D. L. Sivco, J. N. Baillargeon, A. Y. Cho

Research output: Contribution to journalArticle

32 Scopus citations

Abstract

Measurements of NO concentrations at sub-ppm levels in vehicle exhaust are needed for emissions certification of future ultra-low emission vehicles. We demonstrate a wavelength-modulation, laserbased, NO detection system suitable for this purpose. A quantum cascade distributed feedback laser (QC-DFB) operating continuous wave (cw) at ∼100 K is frequency modulated at f = 10 kHz and locked to the center of a transition at ∼1921 cm-1 in the fundamental band of NO. The demodulated signal at 2f of the beam passing through the sample cell directly measures the NO concentration. The cell is a multipass Herriott-type with a 100-m path length. Doppler broadening, pressure broadening, and unresolved A doubling combine to yield a pressure for optimum sensitivity of 100 tort and a modulation amplitude of ∼600 MHz. A flowing gas system is used to avoid problems with adsorption and desorption of NO from the cell walls. The reduced pressure eliminates interference from other gas species. Detection of NO concentrations in the few parts-per-billion (ppb) range is demonstrated in diluted exhaust-gas bag samples collected in the vehicle certification process.

Original languageEnglish (US)
Pages (from-to)706-714
Number of pages9
JournalApplied Spectroscopy
Volume56
Issue number6
DOIs
StatePublished - Jun 1 2002
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Instrumentation
  • Spectroscopy

Keywords

  • Exhaust gas analysis
  • NO detection
  • Quantum cascade laser
  • Tunable laser

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