臺灣博碩士論文加值系統

本論文利用了三個不同的偵測方法來研究雙原子鈉分子系統中的電磁誘發透明現象。利用雙光子共振光譜法，我們建立了兩組階梯式三能階系統 (X^1 Σ_g^+ (15,73)→B^1 Π_u (13,74)→3^1 Π_g (8,75) and X^1 Σ_g^+ (5,55)→B^1 Π_u (9,56)→3^1 Π_g (4,55))，並透過偵測三重態的螢光來確認系統的建立與否。
首先，我們利用一組帶有濾光片的光電倍增管來偵測來自三重態的所有螢光。當電磁誘發透明現象發生時，因為上態的居量分布突然急遽減少，應該能從螢光的偵測訊號中心看到一個明顯的凹陷。但在我們的研究結果中，我們發現因為這個偵測方法的螢光，其產生過程會有一個去相干過程(decoherent process)， 導致像是電磁誘發透明這種與相干性(coherence)有高關聯的現象在這個觀測方法中不易被觀察到。
接著，我們利用單光儀直接量測回到中間態與基態的螢光。在兩組三能階系統中，回到基態的螢光都有被偵測到而且符合計算的波長，但是並不如預期中會受到耦合光(coupling laser, Toptica laser)的影響，而來自上態的螢光更是沒有被偵測到。
在穿透訊號量測方法中，因為我們的系統是使用氬離子雷射(10GHz)的雷射線寬)作為幫浦雷射(在一般的電磁誘發透明系統中是探測雷射)，部分無法被分子吸收的雷射光會造成很大的背景訊號而無法觀察到細微的光強度變化。為了避免這個狀況，我們嘗試去偵測耦合雷射光(Toptica laser, linewidth: 0.5 MHz)的穿透訊號。然而我們依然沒有在此偵測方法中偵測到電磁誘發透明的現象。
縱使本研究目前並沒有在雙原子鈉分子系統中發現電磁誘發透明的現象，我們已提出一個正在進行中的計畫，是利用兩個線寬相當窄的雷射以及與之前不同的能階組合。而我們相信能夠在這個新的系統中，觀察到分子系統中的電磁誘發透明。

We have investigated the electromagnetically induced transparency (EIT) in the diatomic sodium system with three different detection methods. Using the optical-optical double resonance (OODR) spectroscopy, two different combination of ladder-type three-level system in the sodium dimer (X^1 Σ_g^+ (15,73) →B^1 Π_u (13,74)→3^1 Π_g (8,75) and X^1 Σ_g^+ (5,55)→B^1 Π_u (9,56)→3^1 Π_g (4,55)) have been constructed and confirmed by detecting the total fluorescence from the triplet upper state.
First, the total fluorescence signal was detected by a filtered photomultiplier (PMT). Once the EIT occurs, a sharp dip will appear in the middle of the total fluorescence signal because of the sharply decreased population of the upper state. However, the EIT was not observed since the total fluorescence of the triplet upper state is from the population which went through the “decoherent process”; the coherence phenomena such as EIT, is difficult to be observed with this detection method.
Second, either the population of the intermediate state and the upper state was monitored by directly recording the fluorescence back to the intermediate state and ground state respectively through a monochromator. The state-selected fluorescence signals from the intermediate states of two selected three-level system were detected and could be labeled. However, the signal did not be affected by the coupling laser (Toptica laser). Moreover, for the fluorescence signals from the upper state, there was no expected signal appearing in the estimated wavelength.
Since the pump laser (should be probe laser in the ordinary ladder-type EIT) in our system was provided by the Ar^+ laser with 10GHz laser linewidth, the molecules can only absorb certain part of the laser field. Therefore, the transmitted signal of the Ar^+ laser must be accompanied with a large DC background noise. To overcome this problem, we tried to detect the transmitted signal of the Toptica diode laser (coupling laser) which is a narrow band laser (linewidth: 0.5 MHz). However, the EIT phenomena still not be observed in this method.
Although the EIT phenomena was not observed in this study, we have proposed a new system (still diatomic sodium system, but different selected states) which consists of two narrow linewidth tunable ring laser. We believe the EIT phenomena must be observed in such system.

Contents I
List of Figures III
List of Tables VII

Chapter 1 Introduction 1
1.1 Laser Spectroscopy of Sodium Dimer 2
1.2 Electromagnetically Induced Transparency 6
Chapter 2 Theory 9
2.1 Total Energy of Diatomic Molecules 10
2.2 Molecular Term Symbols 14
2.3 Angular Momentum Coupling 17
2.4 Selection Rules 18
2.5 Intensity Distribution 23
2.5.1 Franck Condon Principle 26
2.5.2 Ho ̈nl-London formula 28
2.6 Electromagnetically Induced Transparency 29
Chapter 3 Experiment 37
3.1 Experimental Method 37
3.1.1 Total Fluorescence Detection 37
3.1.2 State-selected Fluorescence Detection 39
3.1.3 Transmitted Signal Detection 40
3.2 Experimental Setup 41
3.3 Heat Pipe 43
3.4 Lasers 44
3.4.1 Ar^+ Laser 44
3.4.2 Diode Laser 44
3.5 Data Acquisition 46
3.5.1 Monochromator 46
3.5.2 Photomultiplier (PMT) 46
3.5.3 Filters 48
3.5.4 Lock-in amplifier 50
3.5.5 Chopper 50
Chapter 4 Results and Discussions 51
4.1 Total Fluorescence Signal 53
4.1.1 Weak transition X^1 Σ_g^+ (15,73)→B^1 Π_u (13,74)→3^1 Π_g (8,75) 53
4.1.2 Strong transition X^1 Σ_g^+ (5,55)→B^1 Π_u (9,56)→3^1 Π_g (4,55) 56
4.1.3 Discussion 58
4.2 State-selected Fluorescence Signal 61
4.2.1 Weak transition X^1 Σ_g^+ (15,73)→B^1 Π_u (13,74)→3^1 Π_g (8,75) 61
4.2.2 Strong transition X^1 Σ_g^+ (5,55)→B^1 Π_u (9,56)→3^1 Π_g (4,55) 64
4.2.3 Discussion 66
4.3 Transmitted Signal Detection 72
Chapter 5 Conclusion 74
Bibliography 78
Appendix 1 - Franck-Condon factors 84
Appendix 2 – Total fluorescence signal 86
Appendix 3 – State-selected fluorescence signal 90
Appendix 4 – Transmitted signal 92

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