二氧化碳光聲光譜之研究

Photoacoustic spectroscopy of CO2 gas

王惠珺(Hui-Jun Wang)

指導教授 ： 施宙聰

國立清華大學/電機資訊學院/光電工程研究所/碩士(2007年)

https://doi.org/10.6843/NTHU.2007.00655

摘要

本論文使用一波長為1570 nm的分佈反饋二極體雷射 (DFB diode laser)，探討二氧化碳氣體的光聲光譜。將雷射光射入至充滿二氧化碳的光聲氣室中，經由光聲效應的作用，將氣體吸收光的變化以聲波的形式呈現，使用電容式麥克風當作壓力換能器，將光聲訊號讀取出來。分別用nondifferential mode 及differential mode 的光聲系統來測二氧化碳在1.57 處附近的吸收譜線R(34)，兩種系統所量測到的靈敏度都約為 ，其中differential mode所量測到的靈敏度，在不同氣室壓力下都比nondifferential mode所量測的靈敏度的好一些，其原因是因為differential PA cell中額外的麥克風可減少同調的雜訊以及環境的背景雜訊。
此外我們也計畫利用共振腔增強方式(cavity enhancement)，提高共振腔內的光強度，進而增強光聲訊號及系統的靈敏度。由於許多技術性問題，目前我們僅能使共振腔之共振頻率在雷射輸出頻率上振盪，尚無法取得光聲光譜訊號。

關鍵字

光聲光譜 ； 二氧化碳

並列摘要

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.

並列關鍵字

photoacoustic ； spectroscopy ； PAS

參考文獻

[1] A.G. Bell, “On the Production and Reproduction of Sound by Light,” Am. J. Sci. 20, 305 (1880)

[2] W. C. Rontgen, “Upon the Production of Sound by Radiant Energy ,”Phil. Mag. J. Sci. 11, 510 (1881)

[3] J. Tyndall, “ Action of an Intermittent Beam of Radiant Heat upon Gaseous Matter,” Proc. R. Soc. 31, 307 (1881)

[4] W.H. Preece,“On the Conversion of Radiation Energy into Sonorous Vibrations ,”Proc. R. Soc. 31, 506 (1881)

[7] E. L. Kerr, and J. G. Atwood, “The laser Illuminated Absorptivity Spectrophone: A Method for measurement of Weak Absorptivity in Gases at Laser Wavelength,” Appl. Opt. 7, 915 (1968)