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Analytical expression for the nth Fourier coefficient of a modulated Lorentzian dispersion lineshape function
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
2011 (Engelska)Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 112, nr 9, s. 1443-1449Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Modulated spectroscopic detection techniques that rely on dispersion, e.g. Faraday modulation/rotation spectroscopy and wavelength-modulated noise-immune cavity-enhanced optical heterodyne molecular spectroscopy, are often described in terms of Fourier coefficients of a modulated dispersion lineshape function. This work derives a non-complex analytical expression for the nth Fourier coefficient of a modulated Lorentzian dispersion lineshape function. The expression is easier to implement, and orders of magnitude faster to execute, than previous approaches involving numerical calculations of integrals. The first six Fourier coefficients are explicitly given and illustrated for their optimum modulation amplitudes, which are also given

Ort, förlag, år, upplaga, sidor
Elsevier, 2011. Vol. 112, nr 9, s. 1443-1449
Nyckelord [en]
Modulated Lorentzian dispersion lineshape, Fourier coefficient, Phase-sensitive detection, Faraday modulation/rotation spectrometry, FAMOS/FRS, NICE-OHMS
Nationell ämneskategori
Atom- och molekylfysik och optik
Forskningsämne
fysik
Identifikatorer
URN: urn:nbn:se:umu:diva-51808DOI: 10.1016/j.jqsrt.2011.02.007OAI: oai:DiVA.org:umu-51808DiVA, id: diva2:488994
Tillgänglig från: 2012-02-07 Skapad: 2012-02-02 Senast uppdaterad: 2018-06-08Bibliografiskt granskad
Ingår i avhandling
1. Faraday modulation spectroscopy: Theoretical description and experimental realization for detection of nitric oxide
Öppna denna publikation i ny flik eller fönster >>Faraday modulation spectroscopy: Theoretical description and experimental realization for detection of nitric oxide
2013 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Umeå: Umeå universitet, 2013. s. 152
Nyckelord
Faraday modulation spectroscopy (FAMOS), Westberg-Wang-Axner (WWA) method, Fourier coefficients, Lineshape asymmetries, Nitric oxide (NO)
Nationell ämneskategori
Atom- och molekylfysik och optik
Forskningsämne
fysik
Identifikatorer
urn:nbn:se:umu:diva-68649 (URN)978-91-7459-616-8 (ISBN)
Disputation
2013-05-14, Naturvetarhuset, N420, Umeå universitet, Umeå, 10:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2013-04-23 Skapad: 2013-04-22 Senast uppdaterad: 2018-06-08Bibliografiskt granskad

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