THE MULTIPHOTON PHOTO-EFFECT AND HARMONIC-GENERATION AT METAL-SURFACES

By using a dipole-layer model for the scattering of electrons at a met al surface in a laser field, we show that, at relatively moderate lase r intensities of some 10(10) W cm(-2) of a Nd:YAG laser, photo-electro ns of very high nonlinear order are generated having energies of up to about 500 eV. Similarly, we predict harmonics of very high order unde r the same parameter conditions. The high-order electron-energy spectr um agrees very well with recent observations by Parkas et al (Phys. Re v. A 41 4123 (1990); Opt Eng. 32 2476 (1993)). With our model predicti ons one does not need to resort to the mechanism of Coulomb explosion in order to explain the observed high-energy photo-electrons.