臺灣博碩士論文加值系統

我們使用磁光阱(Magneto-optical trap, MOT)凝聚了一個低溫銫原子團，數量為5.62×108 個原子，密度為3.03×1011 個/cm3，載入時間為761.81 ms，並在此低溫原子團中量測階梯式的電磁誘發透明(Ladder-type electromagnetically induced transparency)。實驗中使用探測雷射(Probe laser)，從｜62S1/2, F=4＞耦合到中間態｜62P3/2, F'=5＞，和耦合雷射(Coupling laser)，從｜62P3/2, F'=5＞耦合到最終態
｜82S1/2, F=4＞，形成一個三能階系統。在此實驗中，我們將探測雷射頻率固定｜62S1/2, F=4＞到｜62P3/2, F'=5＞的共振頻率上，掃描耦合雷射頻率來得到無背景(background free)的電磁誘發透明光譜。當耦合雷射頻率於雙光子共振頻率時(two-photon resonance)可以得到電磁誘發透明的峰值位置。
我們分別使用抑制與恢復(Suppression and Recovery)和直接偵測探測光束穿透方法來觀察電磁誘發透明窗口的現象。抑制與恢復是當電磁誘發透明發生時原本被探測光束吹散的原子團因吸收降低而導致殘餘在磁光陷阱中的原子數變多，殘餘原子數變多意謂偵測到較強的螢光讀值，因為探測光束要足夠吹走磁光阱中的原子團所以強度不能太弱。適用於強探測光束情況下。而直接偵測探測光束的方式以弱探測光束情況下較為適合，因為太強的探測光束造成原子吸收部分遠小於未吸收部分導致整個電磁誘發透明光譜會有一個背景訊號存在著。實驗發現：直接偵測探測光束穿透的方法在低耦合雷射拉比頻率時可得到較好的訊噪比和較窄的電磁誘發透明窗口。實驗中，當耦合雷射的拉比頻率(Ωc)降低到2.15 MHz時，電磁誘發透明窗口線寬可小至1.72 MHz。此結果與相同實驗參數在室溫電磁誘發透明來做比較，我們發現，在同樣較小的Ωc情況下，低溫原子仍可得到較窄的電磁誘發透明窗口。

We construct the cold cesium atoms, which number is 5.62×108 atoms and density is 3.03×1011 atoms/cm3, by magneto-optical trap (MOT). The loading time is 761.81 ms. We applied the ladder-type electromagnetically induced transparency (EIT) in the cold cesium atoms. The three-level system is coupled by the probe field coupling the states｜62S1/2,F=4＞ and ｜62P3/2,F'=5＞ , and the coupling field coupling the states｜62P3/2,F'=5＞ and ｜82S1/2,F=4＞ .In our experiment, we lock the probe laser frequency from｜62S1/2,F=4＞ to ｜62P3/2,F'=5＞ and scan the coupling laser frequency to receive the background free EIT spectrum when coupling laser frequency is on two-photon resonance.
We observe the EIT window by the methods of suppression and recovery and directly detecting transmission of probe field, respectively. Suppression and recovery apply a probe laser to disperse cold atoms but it will be more residual cold atoms which mean higher fluorescence signal due to EIT. It will be suitable to strong probe laser because probe laser is enough powerful to disperse all of cold atoms in MOT. however, it will be better in low probe regime that I detect the transmission of probe laser directly. Probe laser is too strong that it exists a background signal in EIT spectrum because the absorption is less than part of unabsorption by cold atoms.The results with better signal-to-noise ratio and narrower EIT window are observed by directly detecting the transmission of probe field in lower coupling Rabi frequency. In ladder-type EIT, if the coupling Rabi frequency is lowered to 2.15 MHz, the linewidth of EIT window is narrowed to 1.72 MHz. We still find the smaller EIT linewidth is observed while EIT is applied in cold atoms, in comparison of that in room temperature cell, with the same lower coupling Rabi frequency.

目次 Ⅰ
表目錄 Ⅲ
圖目錄 Ⅳ
中文摘要 Ⅵ
Abstract Ⅶ
誌謝 Ⅷ

第一章 簡介 1

第二章 實驗理論 3
2.1磁光陷阱理論 3
2.1.1 都卜勒冷卻(Doppler cooling) 3
2.1.2 磁光陷阱(Magneto-optical-trap) 5
2.2電磁誘發透明(Electromagnetically induce transparency) 7

第三章 實驗架設 11
3.1 磁光陷阱架設 11
3.1.1 雷射系統 11
3.1.2 真空系統 16
3.1.3 磁場線圈架設 17
3.2 電磁誘發透明系統架設 20
3.2.1 探測雷射(Probe laser) 20
3.2.2 耦合雷射(Coupling laser) 20
3.3 光路架設 21
3.3.1 磁光阱光路架設 21
3.3.2 電磁誘發透明光路架設 21

第四章 實驗結果與分析 23
4.1 磁光陷阱條件量測 23
4.1.1 冷原子團的載入時間 23
4.1.2 冷原子團的數量量測 25
4.1.3 冷原子團的密度量測 27
4.2 電磁誘發透明量測 29
4.2.1 抑制與恢復(Suppression and Recovery) 29
4.2.2 偵測探測光束法 31
4.2.3 光密度(Optical density) 32
4.2.4 頻率校正 34
4.2.5 實驗數據與分析 36

第五章 結論 41

參考文獻 42
附錄一 抑制與恢復數據擬合圖 45
附錄二 直接偵測探測雷射數據擬合圖 47

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