Enhancement of magneto-optical trap of Ytterbium atom via optical repumping of triplet P-states

Abstract

Cold atomic ytterbium (Yb, Z=70) densely captured in a magneto-optical trap (MOT) has opened many possibilities for fundamental studies and applications, including optical frequency standards, parity non-conservation tests, and cold collisional properties. Ytterbium atoms can be cooled and trapped by two types of magneto-optical trapping: the strongly interacting $(6s^{2})^{1}\textrm{S}_{0}$-$(6s6p)^{1}\textrm{P}_{1}$ transition with a laser wavelength of 398.9 nm and the weakly interacting $(6s^{2})^{1}\textrm{S}_{0}$-$(6s6p)^{3}$P$_{1}$ transition with a laser wavelength of 555.8 nm. In this dissertation, we summarize how an ytterbium MOT has been constructed, what are the characteristics of trapped cold Yb gas, and how the performance of Yb MOT has been improved, after a brief review of the principles of Doppler cooling, Zeeman slowing, and magneto-optical trapping.

Radiative decay from the $^{1}\rm{P}_{1}$ state to metastable $^3$P states limits the number of trapped atoms, as well as the $(6s^{2})^{1}$S$_{0}$-$(6s6p)^{1}$P$_{1}$ transition MOT lifetime. Therefore, researchers have attempted to improve the Yb MOT by eliminating the shelving loss characteristics. In this thesis, we report that the atoms associated with the metastable states $(6s6p)^{3}\rm{P}_{0,2}$ are optically repumped, and that the loss rate of the $^{1}$S$_{0}$-$^{1}$P$_{1}$ transition is extracted using trapping laser power-dependent fluorescence measurements. Experiment were performed with and without each repump laser, i.e., a 650-nm laser ($^{3}$P$_{0}$-$^{3}$S$_{1}$) and a 770-nm laser ($^{3}$P$_{2}$-$^{3}$S$_{1}$). The loss rates associated with radiative decay to the metastable states were then analyzed. The experimental results indicate that the number of trapped atoms increases compared to the no-repumping case, by up to 30\%. The repumping has also more than doubled the lifetime of the trapped atoms. The loss rate term was affected by three major physical properties: the bac...