Smith-Purcell radiation emission in aligned nanoparticles

Smith-Purcell (SP) radiation produced by interaction of fast electron beams running parallel to strings of nanoparticles is investigated. Results for the radiation emission probability and electron energy loss spectra using finite and infinite strings of Al and silica spheres are presented. Both of these quantities are obtained by solving Maxwell's equations exactly using a multipole expansion approach. The response of the spheres is described in terms of their local frequency-dependent dielectric functions. In silica, the emission probability is seen to coincide with the energy loss probability within the gap region, where the solid cannot absorb any energy. Large emission rates are predicted for Al, suggesting its possible application in tunable soft uv light generation. The dependence of the emission on the size of the spheres, the string period, and the electron energy is discussed in detail. Finite size effects are also studied for strings of 1-15 Al spheres.