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) from 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 greater than one at b>exp(2w/spl alpha//c) where a is the film thickness and /spl omega/ is the laser frequency. The SPW (/spl omega/, k/sub z/,) can also he excited by a relativistic electron beam, propagating parallel to the interface in the free space region, via Cerenkov interaction when beam energy /spl epsiv/b=(|/spl epsiv/|-1)mc/sup 2/ where /spl epsiv/ is the effective metal permittivity, and mc/sup 2/ is the electron rest mass energy. When the surface has a ripple of wave number k/sub 0/, the SPW (/spl omega/, k/sub zz/) can be excited at lower beam energy via sideband coupling, /spl omega/=(k/sub zz/+k/sub 0/)v/sub b/ where v/sub b/z/spl circ/ is the beam velocity. In both cases, however, the positioning of the beam in the close proximity of the interface is required. The scheme is useful for the generation of wavelengths longer than 1 /spl mu/m.