Climate change and its consequences are one of the most important issues humanity will have to face in the coming decades. Reliable modeling of climate change can only come from an accurate knowledge of the composition of the atmosphere. Over the last 20 years, an unprecedented number of satellite, balloon and ground-based measurement programs have been developed to sound the atmosphere using optical spectroscopy.

However, the current missions face two main issues: the lack of sensitive portable instruments for in-situ spectral acquisitions and the imperfect knowledge we have regarding the spectroscopic signature of molecules present in the atmosphere.

The main goals of my research program are: (1) to develop a portable spectroscopic tool for in-situ detection of atmospheric trace gases, and (2) to measure the absorption parameters of gases of atmospheric importance for use in the analysis of atmospheric spectra and the retrieval of trace gas concentrations.

Trace gas analysis by whispering-gallery mode spectroscopy

This program is aimed at the development of a powerful in-situ instrument to detect pollutants in the atmosphere using a variant of tunable diode laser absorption spectroscopy.  Standard in-situ technique consists of a set of tunable diode lasers, an absorbing medium and a detector. When the laser frequency is tuned over the absorption lines of a gas, a part of the laser intensity is lost when the laser beam passes through the gas. The remaining intensity is measured by the detector at the exit of the absorbing medium and analyzed to obtain the concentration, temperature and velocity of the gaz.

Despite its great sensitivity, the deployment of this technique for atmospheric measurements has been limited because it requires a long path length through heavy multi-pass cell. My plan is to use a new spectroscopic technique based on the whispering-gallery modes (WGMs) of silica micro-resonators to develop a portable sensitive infrared spectrometer for in-situ detection of trace gases. The WGMs are resonance modes in which light is confined, by internal reflection, at the surface of a circular micro-resonator. When the resonator is set inside a gas vapour and its WGM tuned over an absorption frequency of the gas, an energy loss occurs by a non-radiative transfer between the resonator and the neighbouring molecules. As this non-radiative transfer rate is considerably higher than the radiative absorption rate, we can obtain, by analyzing the energy loss, a sensitivity equivalent to those obtained by a bulk device.

Spectroscopic characterization of atmospheric compounds

My current research interests involve the infrared spectroscopy of atmospheric molecules for use in the retrieval of trace gas concentrations from space-borne instruments. I am presently working on the spectroscopic characteristics of CFC-113, an ozone-depleting substance and greenhouse gas and HCFC-142b, a substitute for CFCs, which is also a greenhouse gas.

The two geometrical conformations of CFC-113 (Le Bris et al., 2007)

Those two substances are now detectable by the Atmospheric Chemistry Experiment (ACE), a satellite mission onboard SCISAT-1. However, uncertainties on their infrared signatures lead to large errors on their effective pressure mixing ratio in the atmosphere. My work consists into reducing these errors by simulating in laboratory the atmospheric conditions of temperature and pressure and analysing the infrared response of these molecules. This research in performed in collaboration with the University of Toronto.

• Theoretical calculation of the optical parameters of atmospheric molecules

• Data acquisition and analysis of FTIR spectra of greenhouse gases and ozone depleting substances (CFC-113 and HCFC-142b)

• Implementation of a 2-m long White cell to be coupled with a Fourier transform infrared (FTIR) spectrometer to allow characterization of weak absorption bands of greenhouse gases

Previous

Physical Chemistry: Spectroscopic studies of rare-earth crystals presenting optoelectronic applications

• Experimental study of the spectroscopic properties of crystals by absorption, emission and Raman spectroscopy

• Determination of crystal field parameters and energy levels of the rare-earth ions by numerical computation

• Implementation of photon echo and hole burning spectroscopy experimental setups

Atomic Physics: High-resolution laser spectroscopy experiments in optically-thick Caesium vapor

• Characterisation of two new spectroscopic techniques, the retrofluorescence and the optovoltaic techniques, to analyse vapour–metallic surface interactions

• Data analysis and theoretical modeling of atoms behaviour at the vapour–surface interface

• Numerical simulations and parametric fits of atomic spectra

Atmospheric Physics: Detection of atmospheric HNO3 molecules by high resolution IR spectroscopy

• Parametric fits of experimental data

• Numerical simulation of absorption line shape of methane induced by CO2 laser