This may be a press/publicity release, but it still has quite a bit of information for anyone wanting to catch up on the latest front in free electron laser (FEL). It describes the new DOE funding to look into the next generation of FELs.
I was quite interested in reading about the design of the photoinjector, especially the electron gun. Unfortunately, the article didn't describe exactly what they will be using as the photocathode or the candidate materials they're considering. All they described is that they want something with a high quantum efficiency and other criteria ("...the material must yield a high ratio of electrons to photons, with small emittance, and at the same time hold up under continuous use at hitherto unprecedented repetition rates – in high vacuum and a high accelerating field to boot. A variety of cathode materials will be tested for the new injector....")
The article also has useful link on FELs.