FEL beam metrology with a gas-monitor detector

摘要

For the determination of absolute photon fluxes from high-intense, pulsed VUV and soft X-ray sources like free-electron lasers, a gas-monitor detector system based on the photoionization of rare gases was developed. A prototype system was successfully used for the characterization of VUV free-electron laser radiation at the TESLA test facility (phase 1) in Hamburg. Pulse-resolved measurements at peak powers of more than 100 MW at a wavelength of 87 nm were demonstrated. In order to provide a photon-beam diagnostic of VUV-FEL radiation during phase 2 of the TTF project, a set of four new detectors has been constructed, based on the prototype. The new detector system can be used not only for intensity measurement and monitoring, but also for measuring the beam position. The detector set was calibrated in the Radiometry Laboratory of the Physikalisch-Technische Bundesanstalt at the electron storage ring BESSY II. The calibration was performed using spectrally-dispersed synchrotron radiation at low intensities and a semiconductor photodiode as a transfer standard.