Calibration-free wavelength-modulation spectroscopy based on a swiftly determined wavelength-modulation frequency response function of a DFB laser
2016 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 24, no 2, 1723-1733 p.Article in journal (Refereed) PublishedText
A methodology for calibration-free wavelength modulation spectroscopy (CF-WMS) that is based upon an extensive empirical description of the wavelength-modulation frequency response (WMFR) of DFB laser is presented. An assessment of the WMFR of a DFB laser by the use of an etalon confirms that it consists of two parts: a 1st harmonic component with an amplitude that is linear with the sweep and a nonlinear 2nd harmonic component with a constant amplitude. Simulations show that, among the various factors that affect the line shape of a background-subtracted peak-normalized 2f signal, such as concentration, phase shifts between intensity modulation and frequency modulation, and WMFR, only the last factor has a decisive impact. Based on this and to avoid the impractical use of an etalon, a novel method to pre-determine the parameters of the WMFR by fitting to a background-subtracted peak-normalized 2f signal has been developed. The accuracy of the new scheme to determine the WMFR is demonstrated and compared with that of conventional methods in CF-WMS by detection of trace acetylene. The results show that the new method provides a four times smaller fitting error than the conventional methods and retrieves concentration more accurately.
Place, publisher, year, edition, pages
2016. Vol. 24, no 2, 1723-1733 p.
Atom and Molecular Physics and Optics
IdentifiersURN: urn:nbn:se:umu:diva-117836DOI: 10.1364/OE.24.001723ISI: 000369066300134PubMedID: 26832551OAI: oai:DiVA.org:umu-117836DiVA: diva2:916885