  Fundamental principles of mapping 3-dimensional quasiparticle dispersions in
the valence band using angle-resolved photoemission spectroscopy are discussed.
Such mapping is intrinsically limited in accuracy owing to damping of the final
states, resulting in equivalent broadening in the surface-perpendicular
wavevector. Mechanisms of the intrinsic accuracy are discussed in depth based
on a physically transparent picture involving interplay of the final- and
initial-state spectral functions, and illustrated by photoemission simulations
and experimental examples. Other interesting effects of 3-dimensional
dispersions include 'ghost' peaks in the unoccupied valence band region and
finite peak width at the Fermi level. Finally, optimization of the experiment
on the intrinsic accuracy is discussed.
