Spatial variation of the laser fields and electron dynamics at a gas-solid interface

Abstract

In the long wavelength domain, typically for wavelengths lambda > 100 angstroms, the laser fields are usually taken as independent of the spatial coordinate. However, at the gas-solid interface the electron density of the material and the incident laser fields vary sharply on a scale of few angstroms. Instead of solving Maxwell equations, we present here a theoretical model, called Electromagnetic Fields from Electron Density (EMFED), generating a continuous vector potential from phenomenological relations combining the unperturbed electron density of the material system, the material constants and the laws of optics. As an application of this model, we calculate in a time dependent approach the transition probability and the induced current density between the last bulk state below the Fermi energy and the first image state of a Cu(001) metallic surface. These observables are significantly modified by the spatial variation of the vector potential at the surface. The Coulomb gauge condition, fullfilled everywhere else, breaks down near the surface. The difference between the s- and p- polarizations of the laser field partially unravels this effect.