| Summary: | 碩士 === 逢甲大學 === 光電學系 === 103 === This study used two ways to observe acetylene absorption signal with evanescent wave spectroscopy. One uses 600 nm diameter of fiber taper, the other uses FM heterodyne spectroscopy. According to the theory, we expect two ways can increase SNR of acetylene absorption signal effectively. And then, we observed acetylene absorption signal getting better successfully when we used higher modulation frequency and thinner fiber taper. In order to make a high sensitivity gas sensor, we used different diameter of fiber taper to observe acetylene absorption signal, and we found that acetylene absorption signal better than when we use thinner fiber taper at pressure lower than 1 Torr acetylene.
This work also observed saturated absorption signal with fiber taper successfully too. In order to observe saturated absorption signal clearly, we used tuning fork to carry out the modulation transfer technique, and we observed similar saturated absorption signal without Doppler broadening background at pressure lower than 700 mTorr acetylene.
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