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Faraday rotation spectrometer with sub-second response time for detection of nitric oxide using a cw DFB quantum cascade laser at 5.33 µm
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
2011 (Engelska)Ingår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 103, nr 2, s. 451-459Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

A Faraday modulation spectrometer for sensitive and fast detection of nitric oxide at 5.33 μm utilizing a room temperature continuous wave distributed feedback quantum cascade laser and a Peltier cooled MCT detector is presented. The magnetic field was modulated at 7.4 kHz whereas the laser wavelength was scanned at 20 Hz across the most favorable rotational-vibrational transition for FAMOS, Q3/2(3/2), at 5.33 μm. Using a 15 cm optical path and lineshape fitting, the spectrometer provides a detection limit of 4.5 ppb for a response time of 1 s. An Allan variance analysis demonstrates that the system has an excellent stability, up to several hours of operation.

Ort, förlag, år, upplaga, sidor
Springer, 2011. Vol. 103, nr 2, s. 451-459
Nationell ämneskategori
Atom- och molekylfysik och optik
Forskningsämne
fysik
Identifikatorer
URN: urn:nbn:se:umu:diva-51793DOI: 10.1007/s00340-010-4336-8OAI: oai:DiVA.org:umu-51793DiVA, id: diva2:488713
Tillgänglig från: 2012-02-08 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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