Development of photon beam diagnostics for VUV radiation from a SASE FEL

For the proof-of-principle experiment of self-amplified spontaneous emission (SASE) at short wavelengths on the VUV FEL at DESY a multi-facetted photon beam diagnostics experiment has been developed employing new detection concepts to measure all SASE specific properties on a single pulse basis. The present setup includes instrumentation for the measurement of the energy and the angular and spectral distribution of individual photon pulses. Different types of photon detectors such as PtSi-photodiodes and fast thermoelectric detectors based on YBaCuO-films are used to cover some five orders of magnitude of intensity from the level of spontaneous emission to FEL radiation at saturation. A 1 m normal incidence monochromator in combination with a fast intensified CCD camera allows to select single photon pulses and to record the full spectrum at high resolution to resolve the fine structure due to the start-up from noise.