umu.sePublications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Fast and non-approximate methodology for calculation of wavelength-modulated Voigt lineshape functions suitable for real-time curve fitting
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
2012 (English)In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 113, no 16, 2049-2057 p.Article in journal (Refereed) Published
Abstract [en]

Wavelength modulation (WM) produces lock-in signals that are proportional to various Fourier coefficients of the modulated lineshape function of the molecular transition targeted. Unlike the case for the Lorentzian lineshape function, there is no known analytical expression for the Fourier coefficients of a modulated Voigt lineshape function; they consist of nested integrals that have to be solved numerically, which is often time-consuming and prevents real-time curve fitting. Previous attempts to overcome these limitations have so far consisted of approximations of the Voigt lineshape function, which brings in inaccuracies. In this paper we demonstrate a new means to calculate the lineshape of nf-WM absorption signals from a transition with a Voigt profile. It is shown that the signal can conveniently be expressed as a convolution of one or several Fourier coefficients of a modulated Lorentzian lineshape function, for which there are analytical expressions, and the Maxwell-Boltzmann velocity distribution for the system under study. Mathematically, the procedure involves no approximations, wherefore its accuracy is limited only by the numerical precision of the software used (in this case similar to 10(-16)) while the calculation time is reduced by roughly three orders of magnitude (10(-3)) as compared to the conventional methodology, i.e. typically from the second to the millisecond range. This makes feasible real-time curve fitting to lock-in output signals from modulated Voigt profiles. (C) 2012 Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
Oxford: Elsevier, 2012. Vol. 113, no 16, 2049-2057 p.
Keyword [en]
Voigt lineshape, Wavelength modulation, 2f-signal, Convolution, TDLAS
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:umu:diva-61349DOI: 10.1016/j.jqsrt.2012.05.023ISI: 000309574400009OAI: oai:DiVA.org:umu-61349DiVA: diva2:570676
Available from: 2012-11-20 Created: 2012-11-12 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Faraday modulation spectroscopy: Theoretical description and experimental realization for detection of nitric oxide
Open this publication in new window or tab >>Faraday modulation spectroscopy: Theoretical description and experimental realization for detection of nitric oxide
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Faraday modulation spectroscopy (FAMOS) is a laser-based spectroscopic dispersion technique for detection of paramagnetic molecules in gas phase. This thesis presents both a new theoretical description of FAMOS and experimental results from the ultra-violet (UV) as well as the mid-infrared (MIR) regions. The theoretical description, which is given in terms of the integrated linestrength and Fourier coefficients of modulated dispersion and absorption lineshape functions, facilitates the description and the use of the technique considerably. It serves as an extension to the existing FAMOS model that thereby incorporates also the effects of lineshape asymmetries primarily originating from polarization imperfections. It is shown how the Fourier coefficients of modulated Lorentzian lineshape functions, applicable to the case with fully collisionally broadened transitions, can be expressed in terms of analytical functions. For the cases where also Doppler broadening needs to be included, resulting in lineshapes of Voigt type, the lineshape functions can be swiftly evaluated (orders of magnitude faster than previous procedures) by a newly developed method for rapid calculation of modulated Voigt lineshapes (the WWA-method). All this makes real-time curve fitting to FAMOS spectra feasible. Two experimental configurations for sensitive detection of nitric oxide (NO) by the FAMOS technique are considered and their optimum conditions are determined. The two configurations target transitions originating from the overlapping Q22(21=2) and QR12(21=2) transitions in the ultra-violet (UV) region (227nm) and the Q3=2(3=2)-transition in the fundamental rotational-vibrational band in the mid-infrared (MIR) region (5.33 µm). It is shown that the implementations of FAMOS in the UV- and MIR-region can provide detection limits in the low ppb range, which opens up the possibility for applications where high detection sensitivities of NO is required.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2013. 152 p.
Keyword
Faraday modulation spectroscopy (FAMOS), Westberg-Wang-Axner (WWA) method, Fourier coefficients, Lineshape asymmetries, Nitric oxide (NO)
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-68649 (URN)978-91-7459-616-8 (ISBN)
Public defence
2013-05-14, Naturvetarhuset, N420, Umeå universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2013-04-23 Created: 2013-04-22 Last updated: 2013-04-23Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full text

Authority records BETA

Westberg, JonasWang, JunyangAxner, Ove

Search in DiVA

By author/editor
Westberg, JonasWang, JunyangAxner, Ove
By organisation
Department of Physics
In the same journal
Journal of Quantitative Spectroscopy and Radiative Transfer
Physical Sciences

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 365 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf