Excited States Mapped by Secondary Photoemission

We report on angle-resolved photoemission (ARPES) experiments on Cu(110) using Mg K_<i>α</i> radiation. The secondary emission (SE) fine structure of electrons below 50 eV is found to map the <i>empty</i> band structure relevant for absolute band mapping in ARPES. The finding is based on a direct comparison of our experiments with very low-energy electron diffraction data [Phys. Rev. Lett. 81, 4943 (1998)] recently shown to map the unoccupied states representing the photoemission final-state. This suggests a new theoretical approach to the SE process treating the outgoing electron state as the time-reversed diffraction state.