This is a good brief article on the history and development of the free-electron laser. I think you also get free access to the relevant historical papers being highlighted here. You also get an overview of what they're doing at the LCLS.
The thing that should be pointed out here is that, while they share the same name, i.e. "laser", the regular laser and these free-electron lasers are not under the same domain of study. Regular lasers might fall under atomic/molecular physics, or even solid state physics, whereas free-electron laser falls under accelerator physics because it deals with high energy electron beam and various accelerator structures.