Characterisation of ultrafast x-ray detectors at the European Synchrotron Radiation Facility

With the advent of new x-ray sources, the detection of radiation with picosecond temporal resolution becomes increasingly important. We used the time structure of the radiation at the European Synchrotron Radiation Facility (ESRF) to characterise fast detectors developed for x-ray diagnostics. The detectors tested were neutron pre-irradiated Gallium Arsenide (GaAs) detectors and chemical-vapour-deposited (CVD) diamond detectors. The experiments were performed on beamline BM5, both in single-bunch and multi-bunch mode. The response of the detectors to the hard x-ray pulses was recorded using a single shot 7 Ghz oscilloscope or using a digital oscilloscope in sampling mode. For a current of the electrons in the storage ring of typically 10-15 mA in monomode-bunch, the pulse length was between 100 ps and 150 ps (FWHM). In multi-bunch mode, the X-ray pulse length was independent of the current and shorter. We measured FWHM pulse duration values down to 50 ps. Comparison with data obtained with a streak camera showed that the time resolution of our detectors was at best 25 ps.