  Simulations have shown that space-charge effects can lead to regular
modulation of photoemitted beams in vacuum diodes with gap sizes on the order
of 1 micron and accelerating voltage on the order of 1V. These modulations are
in the THz regime and can be tuned by simply changing the emitter area or
accelerating vacuum field. The average current in the diode corresponds to the
Child-Langmuir current, but the amplitude of the oscillations is affected by
various factors. Given the small size and voltage of the system, the maximum
radiated AC power is expected to be small. In this work we show that an array
of small emitters produces higher frequency signals than a single large emitter
of same area, and how these emitters may be synchronized to produce higher
power signals.
