The role of the nuclear spin in optical pumping withD 2-light

Optical pumping withD ₂-light provides an excellent means for studying collisional relaxation in the excited² P _3/2-state of alkali atoms. Collisional relaxation of orientations in that state very sensitively affects the spin orientation in the ground state. All these orientations may be easily created by absorption of σ⁺- or σ{?{-light. At a certain strength of the relaxation realized by a certain buffer gas pressure, the spin orientation in the ground state even vanishes, providedD ₂-light is used for excitation. The condition for this situation is derived from the set of rate equations which governs the evolution of all the orientations involved. These conditions very markedly depend on the nuclear spin valueI. The validity of this dependence has been checked by magnetic decoupling of the nuclear spin and observing the associated shift of the pressure for vanishing spin orientation.