The dispersion of electronic states near the Fermi level can be measured by angle-resolved photoemission.  In this technique, one typically shines ultraviolet photons on a flat crystal surface and measures emitted electrons as a function of angle, analyzing the electron current as a function of kinetic energy.   Light sources include the He lamp (photon energy 20 eV), synchrotrons (tunable from UV to soft x-ray to hard x-ray), and lasers (6-7 eV). [[review]]