Observation of interference between quadrupole and dipole transitions in low-energy (2-eV) photoionization from a sodium Rydberg state.

Abstract

A measurement of the azimuthal dependence of the angular distribution of photoelectrons from ${13}^{3}$${\mathrm{D}}_{3/2}$-state sodium atoms aligned transversely to the direction of propagation of, and parallel to the direction of linear polarization of, 532-nm ionizing laser radiation, is described. The measured distribution is I(\ensuremath{\varphi})=1+0.026(6)cos\ensuremath{\varphi} where \ensuremath{\varphi}=0 is the direction of the laser beam. This departure from the symmetry I(\ensuremath{\varphi})=const predicted for a pure electric dipole transition is represented theoretically as due to a dipole-quadrupole interference term.