Anomalous photoemission from Ag(100) in the femtosecond regime

We investigate the nonlinear photoemission from a silver monocrystal with femtosecond laser pulses in a wide range of photon energies (0.8 eV<h nu<<6.3 eV). Electrons with high kinetic energy are observed in all cases of nonlinear photoemission and at intensities much smaller than 1 GW/cm(2). In the infrared, the electron distribution resembles a decreasing exponential, the tail extending up to tens of eV. At hnu=3.1 eV such exponential distribution coexists with the Fermi-Dirac distribution due to two-photon emission. An explanation in terms of nanosize protuberancies, heated by localized surface plasmons cannot be ruled out, but alternative pictures, however speculative, are worth being considered.