為了能進行單光子與原子的非線性光學實驗,我們藉由光偶極陷阱提升原子團的光學密度及原子密度。本文探討轉移冷原子到光偶極陷阱的過程,內容包含如何最佳化時間式黑暗型磁光陷阱、空間式黑暗型磁光陷阱與平均時變磁陷阱的實驗參數,以及在不同三種情況下,原子移轉到光偶極陷阱過程的討論。 我們進一步研究如何延長銣原子被捕捉於光偶極陷阱內的儲存時間。若原子分佈於|F = 2>的所有黎曼態,則碰撞造成原子的能態改變,從高能態的|F = 2>躍遷至低能態的|F = 1>,原子得到動能而離開光偶極陷阱。我們將原子儲存在較低能態的|F = 1>或單一黎曼態(|F = 2,m = 2>或|F = 2,m = -2>)可大幅度提升儲存時間,維持光偶極陷阱內原子在特定黎曼態需要於實驗中加入大於4.3 Gauss的均勻磁場。 陷阱深度850 μK的光偶極陷阱下,實驗結果可以捕捉到原子數量為5.6E6、溫度為57 μK。推算陷阱中心原子密度可達6E13cm(-3),換算波長三次方的體積內有120顆原子。
This thesis focuses on transferring cold atoms into an optical dipole trap (ODT). Optical density as well as number density of the cold atoms confined in the ODT can be achieved to a sufficiently high level that is suitable for single-photon nonlinear optics experiments. We studied the processes of loading cold atoms into the ODT from a temporal dark magnetic-optical trap (MOT), a spatial dark MOT, and a time-averaged orbiting potential (TOP) magnetic trap. We further investigated how to prolong the storage time of the atoms captured in the ODT. A rapid loss of the atoms distributed among all the Zeeman states of the hyperfine level |F=2>is due to the hyperfine-changing collision. To increase the storage time, we optically pumped the atoms either to the hyperfine level |F=1> or to a single Zeeman state of |F=2, m=2>or |F=2, m=2>. In the latter case, a uniform magnetic field larger than 4.3 G was applied. We were able to load 5.6106 87Rb atoms with a temperature of 57μK into the ODT with a trap depth of 850 μK from the TOP magnetic trap. Under this condition, the peak number density of the atoms can be as high as 61013 cm-3, i.e. 120 atoms within the volume of 3 where is the wavelength of light.