Laser–matter interaction at solid–gas interface in the A→·p→ gauge: linear and surface terms in desorption

The photodesorption yield from metallic surfaces is calculated using the A→·p→ gauge (notation Ap) for the laser–matter operator in the Hamiltonian with zero scalar potential. At the interface, the spatial variation of the vector potential A→ was determined in the preceding paper from the relation between the dielectric function and the electron density together with the use of the Fresnel conditions. The calculations using the Ap gauge are compared to the standard E→·d→ (notation Ed) laser–matter interaction operator in the dipole approximation, where E→ is constant at the interface. In the Ap gauge a linear term perpendicular, a linear term parallel and a surface term perpendicular to the surface contribute significantly to the laser–matter interaction. The expressions derived for the Ap gauge are implemented in a one-dimensional time dependent Schrödinger equation for the motion of the nuclei and the evolution of the photodesorption of CO from Cu(1 1 1) by a sub pico second laser at an energy of 2 eV was studied. For normal and oblique incidences with p and s polarizations, the desorption yield is calculated. For the Ap gauge the contributions from the above mentioned laser–matter interaction terms are compared with the results using the Ed gauge and thus show significant differences.