Abstract

Two possible mechanisms for the ejection of electrons from a metal surface are a) the well-known "photoelectric effect" and b) thermionic emission. The former process is observed when the energy of the incident photon (ħω) is greater than the work function (A) of the surface; the excess photon energy being transferred to the released electron as kinetic energy. However, when very intense radiation fields are incident upon the surface, new multiphoton phenomena become possible such that nħω > A—an emission process that occurs for both solids and gases. The further phenomenon of above threshold ionization (ATI) in which the ionized electron acquires additional quanta (sħω) from the radiation field is well-known for gas-phase atoms (Agostini et al.¹), but has only been suggested for solids.

© 1994 IEEE