Abstract
The X-ray free electron laser (XFEL) is a novel laser source based on an accelerator system, which is
capable of producing high-power and coherent x- rays. It is an extension of free electron lasers (FELs),
in which a high energy electron beam moving in a periodic magnetic fi eld works as a laser medium.
Although there is no theoretical limit on the lasing wavelength of FEL, the reflectivity of the cavity
mirror sets a practical limit on shortening the available wavelength. In order to break the limit, a new
FEL scheme called self-amplifi ed spontaneous emission (SASE) has been proposed, in which no optical
cavity is required. This paper presents the principle of SASE FEL and its light source performances,
together with the fundamental components in the SASE-based XFEL facility.
