LASER-INDUCED ELECTRON-EMISSION FROM AN AU SURFACE IRRADIATED BY SINGLE PICOSECOND PULSES AT LAMBDA=2.94 MU-M - THE INTERMEDIATE REGION BETWEEN MULTIPHOTON AND TUNNELING EFFECTS

The photoinduced electron emission from the surface of a solid gold target irradiated by single picosecond pulses of an erbium laser is investigated. The applied laser intensity (5-120 GW/cm2) corresponds to the intermediate interaction region between the pure multiphoton and tunnel effects, where the decisive Keldysh-parameter, gamma, is in the range 1 < gamma < 12 = n0. In the light intensity region which is free of surface heating (I(L) < 80 GW/cm2), the slope of the measured logarithmic intensity dependence or the photocurrent decreases from the n0 = 12 perturbative value down to n approximately equal to 5. Therefore the experiment shows that the Keldysh-type theories, which have recently been proved to describe correctly the ionization of atoms, are also valid to a certain extent in the case or the photoeffect in metals.