PhD position Laser Development for Atmospheric Sounding, LIPhy, Grenoble University, France

Detection of radicals in the near-UV by dual-comb spectroscopy

Climate science and atmospheric chemistry have undergone a profound evolution with the development of in situ measurements of various stable elements in the atmosphere, such as methane and CO2. Atmospheric models have been greatly improved by these measurements. Optical methods, capable of rapidly measuring exact concentrations, have largely contributed to this evolution. The challenge remains for the measurement of atmospheric radicals, whose most intense absorption bands are in the near UV range. These highly reactive and unstable molecules, although present in minute concentrations, drive atmospheric chemical reactions. The aim of this thesis project is to take up this challenge within the framework of the RADICALS project, funded by the ANR under the call for tenders "Methodologies, instrumentations, sensors and solutions for the ecological transition". RADICALS is a collaboration between our team at the LIPHY laboratory in Grenoble and two teams from the IGE laboratory in Grenoble and the IPR laboratory in Rennes.

The thesis work will take place mainly in Grenoble, in a team with a long tradition of developing ultrasensitive laser techniques using high-finesse optical cavities. It will involve the development of a near-infrared "electro-optical" frequency comb, based on phase modulation of a single-frequency laser, enabling instant control of the comb's tooth spacing. The idea is to be able of alternating between two spacings over the short light propagation delay between the source and the retro-reflector, in order to obtain a multi-heterodyne signal between the delayed comb and the instantaneous comb (the two having different spacings). This will enable the optical spectrum of the comb to be directly transposed into the radio-frequency domain. This system will be tested and optimized using an optical setup at the IGE, which gives access through a window in their laboratory to a retro-reflector located 5 km away on Mont St-Eynard near Grenoble. The next step will be to convert the electro-optical comb in the visible and near-UV range using non-linear optical methods, so as to be able to target the most intense transitions of atmospheric radicals.

Starting september/october 2024 at: LIPhy (Laboratory of Interdisciplinary Physics), Université Grenoble Alpes / CNRS

Contacts:

Daniele Romanini: daniel.romanini@univ-grenoble-alpes.fr

Guillaume Méjean: guillaume.mejean@univ-grenoble-alpes.fr

Research group web page: https://liphy.univ-grenoble-alpes.fr/en/research/teams/lame-lasers-molecules-and-environment