Nondipole effects in soft X-ray photoemission

Although breakdowns in the dipole approximation in the soft-X-ray photon-energy range (hv < 5 keV) were first observed 30 years ago and have been studied theoretically for many years, their significance at low energies remained generally unappreciated until very recently, when advances in gas-phase-photoemission experiments using synchrotron radiation (SR) began to highlight numerous examples of significant nondipole effects at photon energies as low as tens of eV. This progress report, presented from an experimental perspective, includes a brief history, a description of recent advances, and a look to the future. (C) 2003 Elsevier Ltd. All rights reserved.