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high sensitivity laser spectroscopy of molecular absorption continua

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This thesis is funded in the frame of the ANR project COMPLEAT (COntinuum Measurements for PLanEtary ATmospheres) coordinated by our laboratory and involving two teams of the Laboratoire de Météorologie dynamique. The aim of our project is to characterize by experiment and theory the absorption continua of H2O-CO2, CH4-CO2 and H2-CO2 gas mixture in support of numerical climate simulations of CO2-enriched planetary atmospheres. At present, these continua are mostly unknown. The obtained H2O-CO2 continuum will be implemented at LMD in a 3D Global Climate Model, to understand the role of meteoritic impact events in generating episodic precipitation in ancient Mars.

The H2-CO2 and CH4-CO2 continua measured at LIPhy by ultra sensitivity laser techniques will allow quantifying the amount of CH4 and H2 required to warm early Mars through greenhouse effect. The same continua will be used at LMD to investigate the evolution and observability of planets at the magma ocean stage and to prepare future observations of exo-planets’ atmospheres.
In our group Lasers, Molécules, Environnement (LAME) from LIPhy we are developing state-of-the-art ultra-sensitive laser techniques1 with absorption path lengths equivalent to several hundred km (see The thesis will consist in applying these techniques, and particularly cavity ring down spectroscopy (CRDS), to the measurement of the weak absorption continua of H2O+CO2 and H2+CO2 continua in the CO2 transparency windows near 3.5 µm, 2.3 µm, 1.75 µm and 1.5 µm. This is challenging as it shows up as a small variation of the baseline spectra when the studied gas is injected in the absorption cell. Cavity enhanced absorption spectroscopy techniques are particularly well suited in this context. The same methodology as in our previous works on the measurement of water vapor continua will be applied2. A thermalized high finesse absorption cell will also be developed to determine the temperature dependence of these continua.

The candidate should ideally have knowledge in molecular spectroscopy, laser physics and optics. Skills in LabView programming would be appreciated.
Approximate starting date: October 2020

D. Mondelain
Phone: +33 (0)4 76 51 43 29
Laboratoire LIPhy, 140 rue de la Physique, 38402 Saint-Martin d’Hères