Thèses

Mercredi 15 Décembre 2021 à 14h00.

Spectroscopie UV à Double Peignes de Fréquences (Dual Comb) en vue de l étude de la molécule OH

''The atmospheric gas phase evolution is of main concern for air quality and climate evolution, as indicated in the recent IPPC Report [1]. In this context, the radical OH has been recognized as one of the key molecule in the atmosphere, participating for instance to 90 % of the atmospheric methane loss. The radical OH interactions in the atmosphere remain not fully understood, as it is very challenging to measure. To improve the understanding of the role of OH in the atmosphere, there is a need for instruments that should be sensitive, accurate, and have a fast acquisition time in the timeframe of the OH lifetime (ms). We propose to extend the already existing dual comb spectroscopy (DCS) methodology instrument from the IR [2,3] to the near UV region to take advantage of the strong absorption cross-section of OH at 308 nm. Numerical and theoretical work [4] effectively assess the feasibility of the DCS method in the UV range. This study concludes that the Ti:sa Kerr lens mode-locked laser source appears to be the most adapted laser source to realize DCS in the UV. The advantages of the remote sensing DCS method are multiple: it is a fast acquisition rate with similar sensitivity than the existing spectroscopic methods, it is an in-situ method, free of sampling retrieval and free of atmospheric fluctuations. A homemade DCS laser source has been fully realized in the laboratory with an original geometry. It consists in a single ring cavity laser generating two pulses trains of 100 fs. This geometry is advantageous for DCS as it allows a common noise sharing (amplitude and phase).The total mode-locked emitted output power reaches 700 mW with 5.5 W pump power, which would provide enough power to probe atmospheric molecules with UV-DCS via third harmonic generation. The first tests of the DCS experiment using our homemade laser source have been realized on Fabry-Perot (FP) and O2 molecules. We retrieved accurately the free spectral range of the FP and obtained, with high accuracy, the ro-vibrational transitions position of O2 at 760 nm. We demonstrated that the here developed single cavity laser source provides high enough relative phase stability (at least 330 ms) between the two laser emissions. These first results represent an important milestone towards atmospheric trace gases remote sensing using UV-DCS.

[1] IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J. B. R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu and B. Zhou (eds.)]. Cambridge University Press. In Press
[2] Rieker, G. B., Giorgetta, F. R., Coddington, I., Swann, W. C., Sinclair, L. C., Cromer, C. L., ... & Newbury, N. R. (2013, November). Dual-comb spectroscopy of greenhouse gases over a 2-km outdoor path. In Optical Instrumentation for Energy and Environmental Applications (pp. ET2A-2). Optical Society of America.
[3] Coburn, S., Alden, C. B., Wright, R., Cossel, K., Baumann, E., Truong, G. W., ... & Rieker, G. B. (2018). Regional trace-gas source attribution using a field-deployed dual frequency comb spectrometer. Optica, 5(4), 320-327.
[4] Galtier, S., Pivard, C., & Rairoux, P. (2020). Towards DCS in the UV Spectral Range for Remote Sensing of Atmospheric Trace Gases. Remote Sensing, 12(20), 3444.

Directeur de thèse / thesis director: Pr Rairoux Patrick

Membres du jury / members of the jury:
Dr Picqué Nathalie, Chargée de recherche, Max Planck Institute of Quantum Optics, Munich / Rapporteure
Pr Platt Ulrich, Professeur, Université d’Heidelberg, Institute for Environmental Physics / Rapporteur
Pr Brevet Pierre-François, Professeur, Université Lyon 1, ILM/ Examinateur
Dr Raybaut Myriam, Ingénieure de recherche, ONERA Palaiseau/ Examinatrice
Pr Rairoux Patrick, Professeur, Université Lyon 1, ILM / directeur de thèse
Dr Galtier Sandrine, Maître de conférences, Université Lyon 1, ILM / Co-encadrante de thèse
Dr Hébert Philippe-Jean, Ingénieur de recherche, CNES / Invité

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