High-resolution laser spectroscopy of molecular constituents

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Laser spectroscopy finds numerous applications in the development of optical calibration devices, new gas lasers, trace gas and bio-sensors, and the investigation of atmospheric and astrophysical processes. A new laser spectroscopy laboratory is currently being commissioned at St. Francis Xavier University. Three main projects will be undertaken in this facility: 1. Spectroscopic characterization of atmospheric molecules by mid-IR tunable lasers. The mid-IR region is crucial for trace gas detection, as it corresponds to the spectral region where most molecules have strong absorption bands. A mid-IR tunable laser will be used to characterize the spectral properties of atmospheric trace gases. If we know the spectral signatures of molecules, we can detect them in the atmosphere. 2. In-situ detection of trace gases using whispering-gallery modes (WGM) spectroscopy. At specific wavelengths, light undergoes total internal reflection at the surface of a silica micro-resonator, and becomes confined inside. Whispering-gallery modes resonances correspond to light trapped in circular orbits along the equatorial plane of the micro-resonator. The evanescent part of the light extending outside the micro-resonator is very sensitive to its environment. We can, therefore, detect the presence of a gas around the micro-resonator by a variation of the transmitted light. This new spectroscopic technique presents multiple advantages (high sensitivity, low-cost material, possibility of miniaturisation, etc.) and should allow the development of miniature gas sensors. 3. In-situ detection of protein by WGM spectroscopy. The WGM spectroscopy setup will be adapted for detection of constituents in liquid. In this application, the WGM circulates along the circumference of a thin-walled micro-sized capillary containing the liquid to analyze. The evanescent field extends beyond the interior surface of the capillary and interacts with the constituents of the liquid, creating a shift in the response wavelength. This technique will be applied to protein detection.