Microscopic theory of photoassisted field emission from metals

We derive a general microscopic expression for the photoassisted-field-emission current and the energy distribution curve (EDC) with the help of a nonequilibrium perturbation formalism. It is shown that, in spite of the irreversible nature of the (unperturbed) field-emission system, the EDC at energies above the Fermi level of the emitter is given by the same formal expression as in the pure photoemission case. This EDC is calculated in the simple case of a semi-infinite free-electron emitter. These results are used to discuss what information could be obtained from photoassisted-field-emission experiments concerning the shape of the surface potential and the electronic properties of the cathode.