High-order harmonic generation at metal surfaces in the presence of a strong static electric field

We investigate the generation of high-energy x-ray pulses by irradiating me tal surfaces at grazing incidence with a powerful laser beam in the simulta neous presence of a strong static negative voltage in order to explain expe riments by Farkas et al. (1977, Opt. Commun., 21, 408 and 1988, Opt. Commun , 67, 124). Using the dipole-layer model proposed recently by us to describ e the multiphoton photoeffect at metal surfaces we are able to explain the essential features of the above process, in particular, its dependence on t he strength of the applied voltage and on the power of the laser field used , as well as the maximum photon energy emitted. We also present on the basi s of our model an estimate of the power of the emitted x-rays in fair agree ment with the experimental data.