Light emission from non radiative plasmons excited by electrons on smooth surfaces

Theoretical results are reported on the possibility to observe light emitted from the non radiative surface plasmons which are excited by fast electrons traversing a smooth vacuum-metal boundary. By covering the backside of the metal film with a medium of refractive indexn>1, light can be decoupled from the non radiative plasmons. In the angular intensity distribution this light has a strong characteristic peak exceeding the ordinary transition radiation by a factor of the order of 10².