Abstract
The technical realisation and the commissioning experiments of a high-speed X-ray detector based on a quadrant avalanche silicon photodiode and high-speed digitizers are described. The development is driven by the need for X-ray detectors dedicated to time-resolved diffraction and imaging experiments, ideally requiring pulse-resolved data processing at the synchrotron bunch repetition rate. By a novel multi-photon detection scheme, the exact number of X-ray photons within each X-ray pulse can be recorded. Commissioning experiments at beamlines P08 and P10 of the storage ring PETRA III, at DESY, Hamburg, Germany, have been used to validate the pulse-wise multi-photon counting scheme at bunch frequencies ≥ 31 MHz, enabling pulse-by-pulse readout during the PETRA III 240-bunch mode with single-photon detection capability. An X-ray flux of ≥ 3.7 × 10(9) photons s(-1) can be detected while still resolving individual photons at low count rates.
Highlights
X-ray experiments at synchrotron or free-electron laser (FEL) sources are often limited by the dynamic range and readout time of current detector technologies rather than the peak brilliance of the X-ray source itself
Let us briefly consider the case of a time-resolved ‘optical pump–X-ray probe’ experiment such as sketched in Fig. 1(a), corresponding to a recent application in which we have studied the light-driven out-of-equilibrium dynamics in lipid multilamellar membranes (Reusch et al, 2013a)
In order to fulfil the above requirements, in particular (i), (ii) and (iii), the present approach is based on a quadrant avalanche photodiode (APD; QA4000, First-Sensor AG, Berlin, Germany) operating in the linear regime
Summary
X-ray experiments at synchrotron or free-electron laser (FEL) sources are often limited by the dynamic range and readout time of current detector technologies rather than the peak brilliance of the X-ray source itself. Temporally well defined (‘sharp’) snapshots at a given time delay Át are only obtained if the effective X-ray pulse frequency fb is matched/reduced to the stroboscopic experiment at fpp = 1 kHz. The temporal resolution is in this case, apart from jitter, given by the pulse length of the X-ray source; typical values range from ’ 50 ps for synchrotron sources to 10 fs for FELs. Single-pulse selection by means of high-speed mechanical choppers (Wulff et al, 2003; Cammarata et al, 2008) or gating of modern pixel array detectors (PADs) (Reusch et al, 2013b; Ejdrup et al, 2009), for example at a frequency of fpp = 1kHz, is necessarily accompanied by a tremendous decrease of effective X-ray flux. Analog as well as digital pulse processing has to be achieved in less than 30 ns
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