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Modeling the cavity dispersion in cavity-enhanced optical frequency comb Fourier transform spectroscopy
Umeå University, Faculty of Science and Technology, Department of Physics. (Frekvensskamsspektroskopi.)
2018 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Cavity enhanced optical frequency comb spectroscopy is a technique that allows

for quick and sensitive measurements of molecular absorption spectra. Locking

the comb lines of an optical frequency comb to the cavity modes of an enhancement

cavity and then extracting the spectral information with a Fourier

transform spectrometer grants easy access to wide segments of absorption spectra.

One of the main obstacles complicating the analysis of the measurements is

the inevitable dispersion occurring inside the cavity. In this project, absorption

measurements of CO2 were performed using an existing and well established

setup consisting of a near-infrared optical frequency comb locked to a Fabry-

Pérot enhancement cavity using the Pound-Drever-Hall technique, and a Fourier

transform spectrometer. The purpose was to improve theoretical models of the

measured absorption spectra by creating and verifying a model for the cavity

dispersion, stemming mostly from the cavity mirrors but also from the normal

dispersion of the intracavity medium. Until now, the cavity dispersion has been

treated as an unknown and was included as a fitting parameter together with

the CO2 concentration when applying fits to the absorption measurements. The

dispersion model was based on previously performed precise measurements of

the positions of the cavity modes. The model was found to agree well with

measurements. In addition, pre-calculating the dispersion drastically reduced

computation time and seemed to improve the overall robustness of the fitting

routine. A complicating factor was found to be small discrepancies between

the locking frequencies as determined prior to the measurements and the values

yielding optimum agreement with the model. These apparent shifts of the locking

points were found to have a systematic dependence on the distance between

the locking points. The exact cause of this was not determined but the results

indicate that with the locking points separated by more than about 10nm the

shifts are negligible.

Place, publisher, year, edition, pages
2018. , p. 31
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:umu:diva-157146OAI: oai:DiVA.org:umu-157146DiVA, id: diva2:1295674
Subject / course
Fysik D - examensarbete
Educational program
Master's Programme in Physics
Supervisors
Examiners
Available from: 2019-03-12 Created: 2019-03-12 Last updated: 2019-03-12Bibliographically approved

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Hjältén, Adrian
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CiteExportLink to record
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Citation style
  • apa
  • ieee
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  • de-DE
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  • Other locale
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Output format
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