Characterization and performance evaluation of the XSPA-500k detector using synchrotron radiation

Hybrid photon counting (HPC) detectors are widely used at both synchrotron facilities and in-house laboratories. The features of HPC detectors, such as no readout noise, high dynamic range, high frame rate, excellent point spread function, no blurring etc. along with fast data acquisition, provide a high-performance detector with a low detection limit and high sensitivity. Several HPC detector systems have been developed around the world. A number of them are commercially available and used in academia and industry. One of the important features of an HPC detector is a fast readout speed. Most HPC detectors can easily achieve over 1000 frames s-1, one or two orders of magnitude faster than conventional CCD detectors. Nevertheless, advanced scientific challenges require ever faster detectors in order to study dynamical phenomena in matter. The XSPA-500k detector can achieve 56 kframes s-1 continuously, without dead-time between frames. Using `burst mode', a special mode of the UFXC32k ASIC, the frame rate reaches 1 000 000 frames s-1. XSPA-500k was fully evaluated at the Metrology beamline at Synchrotron SOLEIL (France) and its readout speed was confirmed by tracking the synchrotron bunch time structure. The uniformity of response, modulation transfer function, linearity, energy resolution and other performance metrics were also verified either with fluorescence X-rays illuminating the full area of the detector or with the direct beam.

Counting of Hong-Ou-Mandel Bunched Optical Photons Using a Fast Pixel Camera

The uses of a silicon-pixel camera with very good time resolution (∼nanosecond) for detecting multiple, bunched optical photons is explored. We present characteristics of the camera and describe experiments proving its counting capabilities. We use a spontaneous parametric down-conversion source to generate correlated photon pairs, and exploit the Hong-Ou-Mandel (HOM) interference effect in a fiber-coupled beam splitter to bunch the pair onto the same output fiber. It is shown that the time and spatial resolution of the camera enables independent detection of two photons emerging simultaneously from a single spatial mode.

Advancements towards the implementation of clinical phase-contrast breast computed tomography at Elettra

Breast computed tomography (BCT) is an emerging application of X-ray tomography in radiological practice. A few clinical prototypes are under evaluation in hospitals and new systems are under development aiming at improving spatial and contrast resolution and reducing delivered dose. At the same time, synchrotron-radiation phase-contrast mammography has been demonstrated to offer substantial advantages when compared with conventional mammography. At Elettra, the Italian synchrotron radiation facility, a clinical program of phase-contrast BCT based on the free-space propagation approach is under development. In this paper, full-volume breast samples imaged with a beam energy of 32 keV delivering a mean glandular dose of 5 mGy are presented. The whole acquisition setup mimics a clinical study in order to evaluate its feasibility in terms of acquisition time and image quality. Acquisitions are performed using a high-resolution CdTe photon-counting detector and the projection data are processed via a phase-retrieval algorithm. Tomographic reconstructions are compared with conventional mammographic images acquired prior to surgery and with histologic examinations. Results indicate that BCT with monochromatic beam and free-space propagation phase-contrast imaging provide relevant three-dimensional insights of breast morphology at clinically acceptable doses and scan times.

Development of low-energy X-ray detectors using LGAD sensors

Recent advances in segmented low-gain avalanche detectors (LGADs) make them promising for the position-sensitive detection of low-energy X-ray photons thanks to their internal gain. LGAD microstrip sensors fabricated by Fondazione Bruno Kessler have been investigated using X-rays with both charge-integrating and single-photon-counting readout chips developed at the Paul Scherrer Institut. In this work it is shown that the charge multiplication occurring in the sensor allows the detection of X-rays with improved signal-to-noise ratio in comparison with standard silicon sensors. The application in the tender X-ray energy range is demonstrated by the detection of the sulfur K_α and K_β lines (2.3 and 2.46 keV) in an energy-dispersive fluorescence spectrometer at the Swiss Light Source. Although further improvements in the segmentation and in the quantum efficiency at low energy are still necessary, this work paves the way for the development of single-photon-counting detectors in the soft X-ray energy range.

High Dynamic Range Imaging at the Quantum Limit with Single Photon Avalanche Diode-Based Image Sensors

This paper examines methods to best exploit the High Dynamic Range (HDR) of the single photon avalanche diode (SPAD) in a high fill-factor HDR photon counting pixel that is scalable to megapixel arrays. The proposed method combines multi-exposure HDR with temporal oversampling in-pixel. We present a silicon demonstration IC with 96 × 40 array of 8.25 µm pitch 66% fill-factor SPAD-based pixels achieving >100 dB dynamic range with 3 back-to-back exposures (short, mid, long). Each pixel sums 15 bit-planes or binary field images internally to constitute one frame providing 3.75× data compression, hence the 1k frames per second (FPS) output off-chip represents 45,000 individual field images per second on chip. Two future projections of this work are described: scaling SPAD-based image sensors to HDR 1 MPixel formats and shrinking the pixel pitch to 1–3 µm.

Single Photon Counting Performance and Noise Analysis of CMOS SPAD-Based Image Sensors

SPAD-based solid state CMOS image sensors utilising analogue integrators have attained deep sub-electron read noise (DSERN) permitting single photon counting (SPC) imaging. A new method is proposed to determine the read noise in DSERN image sensors by evaluating the peak separation and width (PSW) of single photon peaks in a photon counting histogram (PCH). The technique is used to identify and analyse cumulative noise in analogue integrating SPC SPAD-based pixels. The DSERN of our SPAD image sensor is exploited to confirm recent multi-photon threshold quanta image sensor (QIS) theory. Finally, various single and multiple photon spatio-temporal oversampling techniques are reviewed.

Enhancing the Linear Dynamic Range in Multi-Channel Single Photon Detector beyond 7OD

We present design, implementation, and characterization of a single photon detector based on 32-channel PMT sensor [model H7260-20, Hamamatsu]. The developed high speed electronics enables the photon counting with linear dynamic range (LDR) up to 10⁸count/s per detector's channel. The experimental characterization and Monte-Carlo simulations showed that in the single photon counting mode the LDR of the PMT sensor is limited by (i) "photon" pulse width (current pulse) of 900ps and (ii) substantial decrease of amplitudes of current pulses for count rates exceeding 10⁸ count/s. The multi-channel architecture of the detector and the developed firm/software allow further expansion of the dynamic range of the device by 32-fold by using appropriate beam shaping. The developed single photon counting detector was tested for the detection of fluorescence labeled microbeads in capillary flow.

Capturing dynamics with Eiger, a fast-framing X-ray detector

Eiger is the next-generation single-photon-counting pixel detector following the widely used Pilatus detector. Its smaller pixel size of 75 µm × 75 µm, higher frame rate of up to 22 kHz, and practically zero dead-time (~4 µs) between exposures will further various measurement methods at synchrotron sources. In this article Eiger's suitability for X-ray photon correlation spectroscopy (XPCS) is demonstrated. By exploiting its high frame rate, complementary small-angle X-ray scattering (SAXS) and XPCS data are collected in parallel to determine both the structure factor and collective diffusion coefficient of a nano-colloid suspension. For the first time, correlation times on the submillisecond time scale are accessible with a large-area pixel detector.

Performance of single-photon-counting PILATUS detector modules

PILATUS is a silicon hybrid pixel detector system, operating in single-photon-counting mode, that has been developed at the Paul Scherrer Institut for the needs of macromolecular crystallography at the Swiss Light Source (SLS). A calibrated PILATUS module has been characterized with monochromatic synchrotron radiation. The influence of charge sharing on the count rate and the overall energy resolution of the detector were investigated. The dead-time of the system was determined using the attenuated direct synchrotron beam. A single module detector was also tested in surface diffraction experiments at the SLS, whereby its performance regarding fluorescence suppression and saturation tolerance were evaluated, and have shown to greatly improve the sensitivity, reliability and speed of surface diffraction data acquisition.