Excitation of surface plasma waves over metallic surfaces by lasers and electron beams

A laser incident on a metal film (deposited on a glass substrate) front the glass side at a specific angle of incidence, excites a surface plasma wave (SPW) at the metal-free space interface. The ratio of the SPW field to the laser field increases with the laser spot size b attaining a value much gr eater than one at b > exp(2 omega a/c) where a is the film thickness and om ega is the laser frequency, The SPW (omega, k(z)) can also be excited by a relativistic electron beam, propagating parallel to the interface in the fr ee space region, via Cerenkov interaction when beam energy epsilon(b) = (\e psilon\ - 1)mc(2) where epsilon is the effective metal permittivity, and mc (2) is the electron rest mass energy, When the surface has a ripple of wave number k(o), the SPW (omega, k(z)) can be excited at lower beam energy via sideband coupling, omega = (k(z) + k(o)) v(b) where v(b) (z) over cap is t he beam velocity. In both cases, however, the positioning of the beam in th e close proximity of the interface Is required, The scheme is useful for th e generation of wavelengths longer than 1 mu m.