Properties of alkali atoms confined in a cold helium gas

Properties of alkali atoms (mainly rubidium and cesium) in a cold helium gas have been extensively studied. Experiments are performed at temperatures down to 1.2 K using alkali-metal vapor cells containing a helium buffer gas, with alkali atoms driven from the cell walls by one of three loading methods: laser ablation, light-induced atom desorption, and spark discharge. For alkali atoms loaded into the cold helium gas, we have found that the relaxation time of the electronic spin of optically polarized rubidium atoms in the ground state is about a minute, much longer than that achieved in conventional vapor cells at room temperature and above. We have also spectroscopically investigated the interactions of excited alkali atoms with helium atoms, especially the formation of alkali-He exciplexes.