Photon Counting Area Detector Research Articles

Detector Tilt Considerations in Bragg Coherent Diffraction Imaging: A Simulation Study

This paper addresses the three-dimensional signal distortion and image reconstruction issues in X-ray Bragg coherent diffraction imaging (BCDI) in the event of a general non-orthogonal orientation of the area detector with respect to the diffracted beam. Growing interest in novel BCDI adaptations at fourth-generation synchrotron light sources has necessitated improvisations in the experimental configuration and the subsequent data analysis. One such possibly unavoidable improvisation that is envisioned in this paper is a photon-counting area detector whose face is tilted away from the perpendicular to the Bragg-diffracted beam during the acquisition of the coherent diffraction signal. We describe a likely circumstance in which one would require such a detector configuration, along with the experimental precedent at third-generation synchrotrons. Using physically accurate diffraction simulations from synthetic scatterers in the presence of such tilted detectors, we analyze the general nature of the observed signal distortion qualitatively and quantitatively and provide a prescription to correct for it during image reconstruction. Our simulations and reconstructions are based on an adaptation of the known theory of BCDI sampling geometry, as well as the recently developed projection-based methods of wavefield propagation. Such configurational modifications and their numerical remedies are potentially valuable in realizing unconventional coherent diffraction measurement geometries, eventually paving the way for the integration of BCDI into new material characterization experiments at next-generation light sources.

Combining a nine-crystal multi-analyser stage with a two-dimensional detector for high-resolution powder X-ray diffraction

The high-resolution powder diffraction beamline at ESRF (ID22), built with a dual-undulator source on the 6 GeV storage ring, combines a wide continuous range of incident energy (6–80 keV) with high brightness, offering the possibility to carry out high-flux high-resolution powder diffraction measurements. In routine operation, a bank of nine scintillation detectors is scanned vertically to measure the diffracted intensity versus 2θ, each detector being preceded by an Si 111 analyser crystal. Although the current detector system has operated successfully for the past 20 years, recent developments in detector technology could be exploited to improve the overall performance. With this in mind, as a test, a two-dimensional Pilatus3 X CdTe 300 K-W pixel detector has been mounted on the arm of the diffractometer, replacing the nine scintillator detectors. At each nominal 2θ value, a two-dimensional image is recorded showing nine distinct regions corresponding to the diffraction signals passing via each of the analyser crystals. This arrangement offers new flexibility in terms of data handling and processing, with the possibility to optimize both peak shape and statistics, to remove parasitic effects, and to gain spatial resolution information. Combining the high efficiency of a hybrid photon-counting area detector with the high angular resolution given by analyser crystals is an effective approach to improving the overall performance of high-resolution powder diffraction.

EXCALIBUR: a small-pixel photon counting area detector for coherent X-ray diffraction - Front-end design, fabrication and characterisation

Coherent X-ray diffraction experiments on synchrotron X-ray beamlines require detectors with high spatial resolution and large detection area. The read-out chip developed by the MEDIPIX3 collaboration offers a small pixel size of 55 microns resulting in a very high spatial resolution when coupled to a direct X-ray conversion segmented silicon sensor. MEDIPIX3 assemblies present also the advantages of hybrid pixel detectors working in single photon counting mode: noiseless imaging, large dynamic range, extremely high frame rate. The EXCALIBUR detector is under development for the X-ray Coherence and Imaging Beamline I13 of the Diamond Light Source. This new detector consists of three modules, each with 16 MEDIPIX3 chips which can be read-out at 100 frames per second in continuous mode or 1000 frames per second in burst mode. In each module, the sensor is a large single silicon die covering 2 rows of 8 individual MEDIPIX3 read-out chips and provides a continuous active detection region within a module. Each module includes 1 million solder bumps connecting the 55 microns pixels of the silicon sensor to the 55 microns pixels of the 16 MEDIPIX3 read-out chips. The detection area of the 3-module EXCALIBUR detector is 115 mm × 100 mm with a small 6.8 mm wide inactive region between modules. Each detector module is connected to 2 FPGA read-out boards via a flexi-rigid circuit to allow a fully parallel read-out of the 16 MEDIPIX3 chips. The 6 FPGA read-out boards used in the EXCALIBUR detector are interfaced to 6 computing nodes via 10Gbit/s fibre-optic links to maintain the very high frame-rate capability. The standard suite of EPICS control software is used to operate the detector and to integrate it with the Diamond Light Source beamline software environment. This article describes the design, fabrication and characterisation of the MEDIPIX3-based modules composing the EXCALIBUR detector.