Plasmon-assisted double-gate field emitter arrays

Electron pulses down to the femtoseconds duration can be generated by exciting metallic nanotips by ultrafast laser pulses. Using an array of metal nanotips, one can generate high-bunch charge pulses with ~10⁷ electrons. Double-gate field emitter arrays with sub-micron pitch nano-tips combined with the surface plasmon polariton resonance of the gate electrode and the beam collimation performance of the stacked-double-gate structure have been proposed recently to further enhance the electron yield and reduce the beam emittance aiming at realizing a ultrabright cathode for the X-ray free-electron lasers and THz vacuum electronic amplifiers, In this work, we present the detailed numerical studies of the proposed structure to elucidate the physical process that enables the efficient tip-laser couplings.