| Summary: | 碩士 === 國立清華大學 === 光電工程研究所 === 95 === In this thesis, we study the photoacoustic spectroscopy of CO2 molecule using a 1570 nm DFB diode laser. The output of a 6-mW DFB diode laser is sent into a photoacoustic cell which is filled with carbon dioxide. Because of the photoacoustic effect, the variation of absorption generates an acoustic wave. We use a microphone as a transducer to detect the photoacoustic signal. An additional photoacoustic system was used to remove the background noise. The sensitivity of the system is , which is comparable with other experiments.
In order to improve the sensitivity of the photoacoustic system, a Fabry-Perot cavity was placed outside the photoacoustic cell to enhance the light intensity. Until now, we are not able to lock the Fabry-Perot cavity on the laser frequency very well due to some technical problems, e.g., the mechanical instability of the cavity. Further improvements are needed to detect the cavity-enhanced photoacoustic signal in the feature.
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