Mode-Expansion Analysis of Evanescent Modes Excited by Electrons Moving above Metal Grating

Electrons moving above a metal grating emit evanescent waves as well as Smith–Purcell radiation. We used a mode-expansion method for analyzing evanescent modes in the optical region. The results calculated in the mode-expansion method were compared to those simulated by a finite-difference time-domain numerical method. Good agreement between the two methods was obtained.