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Implementation of continuous filtering frequency comb Vernier spectroscopy for continuous acquisition of spectra in a flame
Umeå University, Faculty of Science and Technology, Department of Physics.
2017 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

In this project laser absorption spectroscopy was performed on a flame in a Fabry-Pérot cavity, using an optical frequency comb. Optical frequency comb spectroscopy is a technique that allows broadband ultra-sensitive detection of molecular species in gas phase. Optical frequency combs are generated by femtosecond mode-locked lasers, which generate short pulses and whose spectrum consists of a comb of sharp laser lines covering a broad spectral range. Doing spectroscopy with optical frequency combs can hence be compared to measurements with thousand of synchronised continuous wave lasers simultaneously, which enables broadband sensitive measurements in short acquisition times. A Vernier spectrometer uses the filtering ability of the cavity to allow sequential transmission of parts of the frequency comb spectrum. Its technical simplicity and robustness make it a good candidate for measuring in turbulent environments.

The aim of the project was to implement continuous-filtering Vernier spectroscopy in a setup for measuring absorption spectra in air and in a flame. This was done by using an Er:fiber femtosecond laser emitting in the near-infrared wavelength range and a Fabry-Pérot cavity containing the flame. The cavity, which consists of two highly reflective mirrors, lets the light of the comb interact with the molecules in the flame for each of the many round-trips it perform; thus increasing the sensitivity to absorption. An active locking mechanism was implemented to stabilize the coupling of the optical frequency comb to the cavity. The locking allowed multiple measurements to be averaged which reduced noise. A galvanometer scanner was added to the system which was used to measure a broad part of the comb spectrum. Hot water absorption lines were detected in the swept comb spectrum and a candidate absorption peak for OH absorption was recorded.

The spectrometer today has opportunities for improvements. A frequency calibration should be implemented which is essential for making estimates of reactant/product concentrations in combustion processes.

Place, publisher, year, edition, pages
2017. , p. 51
Keywords [en]
optical frequency comb, continuous filtering Vernier spectroscopy
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:umu:diva-142426OAI: oai:DiVA.org:umu-142426DiVA, id: diva2:1161421
Subject / course
Examensarbete i teknisk fysik
Educational program
Master of Science Programme in Engineering Physics
Presentation
2017-11-03, Universitetsklubben, Universums gränd 4, 901 87, Umeå, 14:00 (English)
Supervisors
Examiners
Available from: 2017-12-06 Created: 2017-11-30 Last updated: 2017-12-06Bibliographically approved

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