The SASE FEL at DESY: Photon Beam Diagnostics for the User Facility

We present an overview of the vacuum‐ultraviolet free electron laser (VUV FEL) user facility at DESY comprising the layout of the experimental hall, radiation transport to the experimental area, as well as photon beam diagnostics. In general, diagnostics of the FEL radiation is particularly challenging due to the laser’s unique properties such as extremely high peak powers and short pulse lengths. Yet, pulse‐resolved characterization of the photon beam is essential for most user experiments. In order to monitor important parameters like radiation pulse intensity, spectral distribution, etc. new concepts have been developed allowing efficient use of the new source.