  It is shown that the the interference of above-threshold electron de Broglie
waves, generated by an intense laser pulse at a metal surface yields attosecond
electron pulses. This inerference is an analogon of the superposition of high
harmonics generated from rare gas atoms, resulting in trains of attosecond
light pulses.Owing to the inherent kinematic dispersion, the propagation of
attosecond de Broglie waves in vacuum is very different from that of attosecond
light pulses, which propagate without changing shape. Above the metal surface
there are "collaps bands" and "revival layers" of the electron current even at
macroscopic distances. In the range of parameters considered, the maximum value
of the current densities of such ultrashort electron pulses has been estimated
to be of order of couple of tenths of milliamps per square centimeters.
