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 portable spectroscopic tools 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.

Spectroscopic characterization of trace gases

Measurements of the concentration of atmospheric constituents rely greatly on spectroscopic remote sounding acquisitions from satellite, balloon-borne, or ground-based platforms.  The processing of the raw experimental data is limited by our knowledge of the line positions, intensities, and optical constants of each individual molecule. Incomplete information on some important greenhouse gases currently jeopardizes the remote sounding retrieval. Furthermore, many gases still remain undetected through a total lack of knowledge of their infrared spectra. Intensive studies of the spectroscopic signatures of those trace gases are essential for researchers to take full advantage of atmospheric measurement data.

This ongoing project is to make high-accuracy measurements of greenhouse gases for atmospheric retrieval by mid-infrared tunable quantum cascade laser spectroscopy.  The source is a broadband mid-infrared laser with a spectral range 7.69-11.83 mm. This region covers the atmospheric spectral windows were greenhouse gases are the most potent. There are multiple molecules that require more accurate measurements. Priority is given to those currently detectable by remote sensing from satellites and aircrafts (e.g., glyoxal, methanol, ethene, propyne, formaldehyde, acetone, and formic acid), or those that should soon become detectable (e.g. HFCs).

An interesting additional project is planned in parallel with the same experimental setup. Analysis of the atmosphere of exoplanets is a field in expansion. First results had showed a surprising variety of atmospheric compositions with dominant gases such as ammonia, methane and acetylene. New programs like FINESSE (Fast INfrared Exoplanet Spectroscopic Survey Explorer) may likely provide a large amount of raw data in the mid-infrared. Proper analysis of those data will depends on the availabilities of spectra broadened by exotic molecules. Acquisitions of experimental reference spectra will be soon performed in this facility.

Cavity-enhanced absorption and whispering-gallery mode spectroscopy

The analysis of atmospheric raw data from remote measurements depends strongly on the retrieval techniques used to extract the information. This can result in important discrepancies between different instruments and requires extensive validation efforts. In situ measurements of trace gas concentrations from balloon-borne or aircraft missions offer a solution to this problem by providing both precise volume-mixing ratio of trace gases at local geographical points and accurate reference values for remote sounding missions. Nevertheless, in situ measurements have always been limited mostly by the heaviness and cost of the payload missions.

New portable instruments need to be developed to face this issue and allow a more extensive use of this technique. Miniature lasers, detectors, and electronic components are already commercially available. The current main size limitation is the length of the cavity. But this difficulty can now be overcome by recent laser spectroscopy techniques. Two techniques −cavity-enhanced absorption (CEA) spectroscopy (also called ICOS for Off-axis Cavity Output Spectroscopy) and whispering-gallery modes (WGM) spectroscopy− have shown promising results. This project aims to apply these techniques to the mid-infrared spectral region where molecules have their strongest signatures.

Capabilities

A new state-of-the-art facility, the Laser spectroscopy Laboratory, has been built to undertake my research program. This laboratory was mostly funded by the Canadian Foundation for Innovation (CFI) – Leader Opportunity Funds (now renamed John R. Evans Leaders Fund), the Nova Scotia Research and Innovation Trust (NSRIT) matching funds, and a NSERC Discovery Grant.

The masterpiece of the laboratory is a new tunable mid-infrared laser, the MIRcat^TM from Daylight Solutions. This powerful laser has one of the largest broadband currently available in the mid-infrared and covers a spectral area corresponding to an important atmospheric spectral window.

 

Ongoing collaborative research program

In collaboration with Prof. Kimberly Strong and her research group at the University of Toronto, we have developed a research program to improve the reliability of data parameters and infrared cross-sections of greenhouse gases and ozone-depleting substances.

 

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

This program includes:

• Theoretical calculation of the optical parameters of atmospheric molecules

• Data acquisition and analysis of Fourier transform infrared spectra of greenhouse gases and ozone depleting substances.

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