AC Stark shift of an alkali-metal atom in a laser beam has a Zeeman-like term, which is proportional to the vector polarizability , in addition to a usual scalar ( ) term. I will discuss a few experiments using to manipulate ground-state alkali-metal atoms:
(i) When the laser is circularly polarized and properly tuned between the D1 and D2 transitions, the term vanishes and the Stark shift takes the form of a pure Zeeman shift. We constructed an optical analog of a magnetic trap and carried out an optical Stern-Gerlach experiment.
(ii) For the atoms in an optical trap, a differential ac Stark shift of a ground-hyper ne transition can be tuned out by adjusting polarization of the trapping eld. By using the \magic polarization" for 7Li, we achieved 0.6 Hz linewidth. I will describe how we use the capability to manipulate atoms in an optical lattice in a site-speci c manner.
(iii) In a circularly-polarized optical trap, hyper ne-transition frequency of an atom depends on the vibrational quantum number n. I will describe our experiments to develop new schemes to cool optically trapped atoms using the n-dependence: RF-induced evaporative cooling in an optical trap and \motion-selective" CPT cooling which is analogous to the velocity-selective CPT cooling.