Surface photoeffect: photoabsorption of surface and image states

The surface photoeffect of Al( 001) is studied for a p continuous laser in the long wavelength ( LWL), i.e. lambda >= 100 angstrom. Perpendicular to a gas-solid interface the potential, the electron density, and consequently the laser fields, vary at the atomic scale and the LWL approximation, corresponding to constant in space laser fields, does not apply. The vector potential associated with these laser fields, written in the temporal gauge U = 0, is obtained by solving the Maxwell and the material equations. In the present model the dielectric function, entering these material equations, is dependent on the electron density rho( z) perpendicular to the surface calculated from the Schrodinger equation and on the bulk dielectric constant. Using these calculated spatially varying laser fields, the photoabsorption spectrum of the surface, the Fermi and the first image states of Al( 001) are calculated using the Fermi golden rule. For the first time in the case of a realistic potential, the photoabsorption yield is analysed in terms of the standard velocity, the surface and the interference contributions. All these terms contribute significantly to the total yield and this yield, calculated up to 25 eV, compares fairly well with the experiment.