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Shirmohammad, Maryam

University of British Columbia

Raman spectroscopy is a fingerprint type analytical tool for gas analysis. Raman spectroscopy of gases is challenging due to their low number density, in addition to the intrinsically weak probabilities of Raman scattering. Incorporating enhancement techniques is essential for Raman analysis of gases. An effective enhancement technique commonly used for gas samples, is fiber enhanced Raman spectroscopy (FERS), where the intensity of spontaneous Raman scattering is enhanced by confining gas and a CW laser light inside the core of a hollow core photonic crystal fiber. The first objective of this thesis was to investigate whether single beam pulsed laser excited stimulated Raman scattering (SRS) based FERS can function as an enhancement technique for gas analysis. Therefore, a FERS system was developed with a nanosecond pulsed laser as the excitation pump. Initial studies were performed with simple gases such as H₂ and CO₂ and the results confirmed that single beam SRS-FERS results in orders of magnitude enhancement of Raman intensities from the gases. Raman intensities grow exponentially with pulse energy and gas pressure. In the next step, single beam SRS-FERS was applied to propene, a VOC (volatile organic compound) of metabolic association and measurements showed an exponential growth of Raman intensities as a function of pulse energy and gas pressure. This confirmed the potential of SRS+FERS for breath component analysis for cancer diagnosis through analysis of VOC biomarkers of breath. The second objective of this thesis was evaluating the collision between two different gas particles as an enhancement of Raman scattering intensities of analyte gas. Exploratory experiments were performed with H₂, and CO₂ mixed with He/N₂. The results were surprising as upon mixing the gases with He/N₂, the intensity of Raman scattering grew exponentially with pressure of He/N₂. Raman studies were performed with propene at a very low pressure mixed with He, and the results confirmed that indeed collision enhanced Raman scattering (CERS) functions as an ultra-efficient enhancement mechanism for analysis of trace amount gases. This novel technique can be used to improve the detection limit of Raman system significant for breath VOC analysis.

Text

2023-09-30

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/79296

Physics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/