  A new type of negative electron affinity (NEA) photocathode based on GaAs
nanopillar array (NPA) Mie-type resonators was demonstrated for the first time.
For visible wavelengths, the Mie resonances in GaAs NPA reduced light
reflectivity to less than 6 percent compared to a typical value great then 35
percent. Other benefits of NPA resonators include an enhanced density of
optical states due to increased light concentration and increased electron
emission area. These features resulted in improved photoemission performance at
the resonance wavelength demonstrating maximum quantum efficiency 3.5 times
greater than a GaAs wafer photocathode without the NPA structure. This
optically dark photocathode (sub-percentage light reflectance over visible
wavelengths) but possessing electrically high-brightness (enhanced electron
emission) provides new opportunities for practical applications such as
large-scale electron accelerators, high-resolution night-vision imaging and low
energy electron microscopy.
