Measuring nondipolar asymmetries of photoelectron angular distributions

In theories of photoelectron angular distributions at soft-x-ray energies from 1 to 10 keV, first-order corrections to the dipole approximation give rise to two nondipolar asymmetry parameters in addition to the well-known dipolar asymmetry parameter β. The nondipolar parameters characterize the forward-backward asymmetry with respect to the propagation vector of the photon beam. Experimentally, the measurement of the nondipolar effect has been hampered because of the complications resulting from the three-parameter angular distribution. In this paper, we suggest various experimental approaches to the measurement of the three asymmetry parameters using partially linearly polarized x rays, corresponding to measurements on synchrotron radiation beamlines. We describe methods to extract the asymmetry parameters using such approaches. copyright 1996 The American Physical Society