There is a news feature article on X-ray free electron lasers in Nature magazine describing the powerful X-ray lasers —Nature 505, pp 605 (2014). The article gives a good historical account of the challenges faced by the XFELs and the first exciting results obtained at the LCLS in Stanford. You can download the entire PDF here. This is part of a special issue dedicated to crystallography as “Crystallography turns 100″ — Nature 505, pp 585-716 (2014).