Affordable High Yield Photocathodes for FEL Injectors
Navy SBIR FY2008.2

Sol No.: Navy SBIR FY2008.2
Topic No.: N08-162
Topic Title: Affordable High Yield Photocathodes for FEL Injectors
Proposal No.: N082-162-0613
Firm: Saxet Surface Science
3913 Todd Lane
Suite 303
Austin, Texas 78744-1057
Contact: Gregory Mulhollan
Phone: (512) 462-3444
Web Site:
Abstract: 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.
Benefits: In addition to supplying the required photoemitters to the Navy for their FEL injectors, other FEL based systems will benefit from the amorphous silicon germanium photocathodes. Accelerators such as energy recovery linacs will find amorphous silicon germanium use very inviting. Reliable, low cost photocathode driven RF gun systems could become ready replacements for the diode and triode guns used on medical accelerators for production of clinical photon beams and therapy electron beams. An integral photon source can be packaged with a transmission mode photocathode to allow both much better capture efficiency over the presently employed DC gun sources and beam control without requiring a high voltage pulser. We have already made significant strides toward integrating amorphous silicon photoemitters into microphotonic vacuum tubes, a potentially very large market.