Affordable High Yield Photocathodes for FEL Injectors

For FEL based systems to become practical as weapons, it is necessary photoinjectors be used to generate the low emittance, high current, high peak charge electrons needed for photon production. Higher overall system reliability can be achieved if the photoemitter operates in the visible wavelength range. Photocathodes are consumables in the operation of an FEL injector gun and are required to be made as reliable, inexpensive and simple to use as possible. Amorphous silicon germanium shows great promise as a negative electron affinity visible wavelength photocathode suitable for FEL gun systems. Advantages of amorphous silicon germanium include a high degree of immunity to charged particle flux, low thermal emittance, bandgap tunability and low production cost. Amorphous silicon germanium can be readily grown on a variety of substrates including those transparent at its bandgap enabling transmission mode as well as reflection mode photocathodes to be fabricated.