| Summary: | 碩士 === 國立交通大學 === 電子物理系 === 89 === Utilizing Raman spectroscopy technique, we use a 532-nm, 5-mW average power, passive Q-switch microchip laser to measure aqueous methanol of different concentrations. In order to lower the detection limit, we use a liquid waveguide to enhance the liquid Raman signal and a cooling system to reduce the thermal noise from photomultiplier tube (PMT). The goal of this dissertation is to construct a Raman spectroscopy system utilizing the pulsed microchip laser and to analyze the detection limit of the system in terms of the concentration methanol. In this experiment, a boxcar integrator system is used to grab the pulsed Raman signal triggering by the laser source. The measured detection limit of methanol concentration are 5% by using quartz cell and 0.5% by using liquid waveguide, separately.
It is believed that the detection limit of aqueous concentration could be further reduced if we use a higher power microchip laser. With the advantages of compactness and portability, we hope this system to be used in real time monitoring the pollution of rivers.
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