臺灣博碩士論文加值系統

本論文主要是討論一氧化碳光阻抗光譜以及在一氧化碳雷射頻率穩定的應用。論文中報告了直流跟射頻光阻抗光譜的研究成果，同時也利用蘭姆凹陷改進雷射頻率的穩定度。
由於清晰的蘭姆凹陷是改進雷射頻率穩定度的關鍵因素，如何得到便成為本論文中的重要課題。蘭姆凹陷很容易因為氣壓噌寬的效應變得很淺甚至消失，能夠在低氣壓下獲得低雜訊的射頻光阻抗光譜便成為一個很值得考慮的光譜方法。在過去的研究中我們也的確如預期地看到蘭姆凹陷，整個吸收訊號的訊噪比大約是2190，利用一次微分解調光譜，我們可將一氧化碳雷射的頻率穩定度提升到小於300 kHz。
在實驗中，我們也發現了對於某些特定的雷射譜線，存在一些異常的光阻抗光譜訊號，這些訊號的強度遠大於其他的訊號。目前這些訊號的來源依舊不明，需要更進一步的探討。

The optogalvanic spectroscopy of carbon monoxide moleucle (CO) and its application on frequency stabilization of CO laser are presented in the dissertation. Both DC and RF optogalvanic spectroscopy were studied and the saturation dip was pursued for the better frequency accuracy and stability.
The DC optogalvanic spectroscopy was first studied in a low pressure discharge tube which the gas mixture of CO, N2 and various noble gases flowed through. The operating pressure was kept between 0.8 and 1.3 Torr to reduce the pressure broadening; the positive column region of the discharge was cooled to -60 C. The optimal S/N ratio was about 600 with the gas mixture CO : N2 : Ar = 1 : 84 : 11 and the total pressure was 1.344 Torr. No saturation dip was observed yet. It was believed that the pressure broadening should be responsible for the missing saturation dip.
The RF optogalvanic spectroscopy was studied in order to lower operating pressure. There were three different RF circuits were constructed. Two of them were based on the design of Colpitts oscillator and one was based on a push-pull oscillator. Low or no nitrogen concentration was preferred for RF optogalvanic signal. All three circuits could operate down to 600 mTorr with little noise degradation. Cooling the discharge tube by spraying liquid nitrogen was once tested on Colpitts-I circuit and severely lowered the signal. The maximum S/N ratio was about 2190 for Colpitts-II circuit at amplitude modulation frequency 255 Hz. The saturation dip was observed by both Colpitts optogalvanic circuits and the depth was typically less than 5%.
By wavelength modulation technique, the frequency of CO laser could be stabilized at the zero points, which was corresponding to the absorption line center of CO, of derivative spectroscopic signal. The limit of frequency stability was about 149 kHz and the practical stability was better than 300 kHz when the laser was stabilized by first order derivative
spectroscopic signal. The third order derivative spectroscopic signal was also obtained but not used to stabilize laser frequency due to low S/N ratio.
The extraordinary optogalvanic signals around some specific CO laser wavelengths were only found by Colpitts-II circuit. The origins of these extraordinary signals were discussed but yet identified.
At last, the outlook of the experimental works is presented.

Summary i
1 Introduction 1
1.1 Retrospect of CO laser frequency Stabilization
1.2 Organization
2 Rotation-Vibration Spectroscopy of CO
2.1 The Problem of Conventional Spectroscopy
2.2 Optogalvanic Spectroscopy
2.2.1 Retrospect
2.2.2 Temperature Perturbation Model
2.2.3 A Simple Plateau Model of OGE
3 Apparatus
3.1 Carbon Monoxide Laser
3.1.1 Mechanical
3.1.2 Electronics
3.1.3 Cooling and Gas Filling
3.2 Optical System
3.3 Electronics
3.3.1 DC Electronics
3.3.2 RF Electronics
3.3.2.1 Basic of Oscillator
3.3.2.2 AM Demodulators
3.3.2.3 Colpitts-I Oscillator
3.3.2.4 Colpitts-II Oscillator
3.4 Vacuum System
4 Experimental Results and Discussions
4.1 Parametric Studies of Optogalvanic Spectroscopy
4.1.1 Brief Review of the Results for DC and Colpitts-I Circuits
4.1.2 INER Circuit
4.1.3 Results for Colpitts-II Circuits
4.2 Frequency Stabilization
4.3 Extraordinary Optogalvanic Spectral Lines
5 Outlook
A Worksheet for Beam Propagation
B Parts List and Artworks

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