  Nonlinear photoemission from a silver single crystal is investigated by
femtosecond laser pulses in a perturbative regime. A clear observation of
above-threshold photoemission in solids is reported for the first time. The
ratio between the three-photon above-threshold and the two-photon Fermi edges
is found to be 10^{-4}. This value constitutes the only available benchmark for
theories aimed at understanding the mechanism responsible for above-threshold
photoemission in solids.
