  Theory of electron emission by metallic photocathodes under the exposure of
long wavelength lasers will be studied. Energy of photons in long wavelength
lasers is less than the work function of the photocathode material, and can
only emit electrons via tunneling through the potential barrier. The optical
resonance effect (e.g. plasmonic resonances) will be studied as an improvement
to the performance of photocathodes. This paper is intended to provide
self-sufficient materials to design optical resonant surfaces (e.g.
metasurfaces) for electron emission applications.
