臺灣博碩士論文加值系統

冷原子（在此指的是小於 1 mK 的溫度下），不同於熱原子的物理現象，可以有效減低環境所造成的影響，例如都卜勒頻寬（Doppler Broadening）、熱擴散（Thermal Diffusion）、碰撞微擾（Collisional Perturbation）等許多由熱效應所造成的干擾現象。為了研究冷原子的現象，我們在雷射冷卻中選用普遍且有效的方式：磁光陷阱（Magneto-Optical Trap）來捕捉銣（87Rb）的冷原子。磁光陷阱，主要是在空間中三個維度上，安排六道雷射光和一組反向赫氏線圈（Anti-Helmholtz Coil），使原子減速並限制在六道雷射光的交會處。我們藉由光學幫浦（Optical Pumping）的方式來量測磁光陷阱中捕捉的冷原子數量，研究原子數的變化與磁場梯度、陷阱雷射（Trapping Laser）的紅調變（Red Detuning）、功率、光束大小的關係；並且研究了回幫浦雷射（Repumping Laser）的強度以及幫浦雷射（Pumping Laser）強度、偏振等改變與原子數的關係。經由我們的磁光陷阱系統最佳化的結果，可以量測到 (5 ± 0.5) ×10^9 顆冷原子。

The influence of environment is efficiently reduced in cold atoms (< 1 mK), compared with thermal atoms (~ 300 K). For example, doppler broadening, thermal diffusion, collision perturbation and other temperature-related nuisances are greatly reduced at such low temperature. In order to study the phenomena at such a low temperature, a magneto-optical trap (MOT) is a rather simple method to produce cold atoms. In the MOT system, the number of trapped atoms is related to red detuning, magnetic field gradient, light alignment and laser power, etc.. In this work, we have investigated how the number of trapped atoms varied with the trapping laser detuning, laser power, laser beam size and magnetic field gradient. Furthermore, we also demonstrated the variance of number of trapped atoms by adjusting the power of repumping laser and pumping laser, and polarization of pumping laser. Finally, the maximal number of trapped atoms in our MOT system is (5 ± 0.5) × 109 at magnetic field gradient of 14 Gauss/cm and detuning of 24 MHz.

摘要................................................................................................................i
Abstract.........................................................................................................ii
致謝...............................................................................................................iii
目錄...............................................................................................................iv
圖目錄............................................................................................................vi
表目錄..........................................................................................................viii

緒論...............................................................................................................1
基本原理.........................................................................................................2
2.1 銣能階與特性.........................................................................................2
2.2 飽和吸收...............................................................................................6
2.2.1 飽和吸收光譜................................................................................6
2.2.2 交錯訊號.......................................................................................8
2.3 鎖頻系統.............................................................................................10
2.4 磁光陷阱.............................................................................................12
2.4.1 都卜勒冷卻...................................................................................12
2.4.1 磁光陷阱......................................................................................15
2.5 原子數量測：光學幫浦法.......................................................................18
實驗系統架設................................................................................................20
3.1 真空系統與銣原子源..............................................................................20
3.1.1 真空系統......................................................................................20
3.1.2 銣原子源......................................................................................23
3.2 飽和吸收光路架設.................................................................................24
3.3 磁光陷阱系統架設.................................................................................28
3.3.1 陷阱雷射......................................................................................29
3.3.2 回幫浦雷射...................................................................................33
3.3.3 雷射光偏極與磁場..........................................................................35
3.4 光學幫浦系統架設.................................................................................38
實驗結果與分析.............................................................................................41
4.1 系統時序設計.......................................................................................41
4.2 陷阱雷射紅調變、磁場梯度與原子數最佳化..............................................42
4.3 陷阱雷射功率、光束大小與原子數關係....................................................44
4.4 回幫浦雷射強度與原子數關係.................................................................47
4.5 幫浦雷射強度、偏振與原子數關係...........................................................48
5. 結論與展望................................................................................................50

參考資料.......................................................................................................51
附錄 A：稜鏡對製作.......................................................................................53
附錄 B：光隔離器原理及架設...........................................................................55
附錄 C：四分之一波板原理及架設....................................................................57
附錄 D：地磁補償線圈製作.............................................................................59
附錄 E：系統總架設光路.................................................................................64
附錄 F： 87Rb、85Rb 元素 D1、D2 躍遷 C.G. 係數表......................................65
附錄 G：固態繼電器測試.................................................................................72

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