Date of Award
Eutrophication;Kerr-instability amplification;Laurentian Great Lakes;Phosphorus;Raman spectroscopy;Stimulated Raman spectroscopy
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The eutrophication of freshwater ecosystems remains a persistent global problem threatening biodiversity, drinking water, and economic interests. Among the Laurentian Great Lakes, Lake Erie is most severely impacted by eutrophication, experiencing annual harmful algal blooms that are thought to result from excess phosphate deposition into the ecosystem. Efforts to study and mitigate the effects of eutrophication require accurate monitoring of phosphate concentrations. The current method for measuring phosphate, the molybdenum blue method, suffers from signal interference. In this thesis, I recommend Raman spectroscopy as a label-free, reagent-free spectroscopic technique for accurately measuring phosphate in freshwater. I verify the Raman spectrum of dissolved phosphate using a Raman microscope, but find the signal to be weak, making it impossible to detect low concentrations in the environment. I, therefore, turn to stimulated Raman spectroscopy (SRS) to enhance the signal and improve the signal-to-noise. I develop a novel method for broadband SRS using Kerr-instability amplification (KIA) to generate the broadband Raman probe spectrum. I show via numerical simulations and experiments that KIA can be treated as an extension of four-wave mixing and can amplify supercontinuum spectra. I prove that the amplified spectrum from KIA can be used as a Raman probe spectrum by making the first reported SRS measurement of 1-decanol, and I show preliminary data for detecting dissolved phosphate. I generate an ultra-broad Raman probe spectrum spanning the OH, fingerprint, and THz regions that shows promise for detecting dissolved phosphate and other important chemicals in the Great Lakes.
Drouillard, Nathan Gregory, "Stimulated Raman Spectroscopy with Widely Tunable Probe Pulse for Measuring Dissolved Inorganic Phosphorus in the Great Lakes" (2024). Electronic Theses and Dissertations. 9194.