Single Photon Counting Mode Research Articles

Ultrawide Dynamic Sensing from Single‐Photon Counting to Linear Detection Using a Segmented Superconducting Nanowire

AbstractDespite their exceptional sensitivity, single photon detectors typically exhibit limited tolerance to strong light compared to conventional linear photodetectors. Consequently, a disparity arises between these two detector types, hindering the achievement of both high sensitivity and high dynamic range in sensing and imaging. To bridge this gap, a segmented architecture is implemented with a waveform‐variance readout scheme for extacting high‐flux photon informaiton.This approach gives an unprecedented ultra‐high dynamic range of 75 dB at a fixed bias current, where single photon counting mode and quasi‐linear photodetection mode coexist. High‐dynamic imaging, passive thermal imaging, and joint active and passive imaging are demonstrated, which validate the advantages of this dual‐mode detector. Such a versatile detector will offer enhanced flexibility, single‐photon sensitivity, as well as ultra‐wide dynamic range across various scientific and technical domains.

Quantitative analysis of silicon photomultipliers for thermoluminescence measurement

The employment of silicon photomultipliers (SiPMs) in photon detection systems facilitates the reduction of detection module size, enhances portability and ruggedness, and lowers product costs. This study investigated the potential of SiPM in thermoluminescence (TL) measurements, focusing on its detection limits, temperature dependency, and dose responses. A 3 × 3 mm2 multi-pixel photon counter (MPPC, Hamamatsu MPPC) composed of 50 μm single-photon avalanche diodes (SPADs) was utilized in single-photon counting mode as the detector. This experimental setup was compared with a conventional photomultiplier tube (PMT) in TL readout case. To ensure comparable light exposure between the two detectors, a 3-mm diameter pinhole was positioned in front of the PMT. By using a thermoelectric (TE) cooling module to maintain the sensor temperature at −20 °C, signal reproducibility was achieved with a fluctuation of less than 1.2%, and a detection limit ranging from 30 to 300 μGy was assessed for four dosimeters: LiF:Mg,Ti, LiF:Mg,Cu,P, LiF:Mg,Cu,Si, and Al2O3:C. The dose response of the system was limited by significant signal saturation due to pile-up effects. We introduced a correction model with a 50 ns paralyzable deadtime, which enhanced the signal response by more than 20-fold. Furthermore, this model also correlated well with the observed count rates under high dark count rate (DCR) conditions up to 1.67 MHz. The findings from this study further contributes to the discussion regarding the perspective of SiPM as TL detectors.

A prototype Radiation Energy Measuring Integrated Circuit with an asynchronous current-pulse reset block providing analog-to-digital conversion in 28 nm CMOS

In this paper we introduce a prototype Radiation Energy Measuring Integrated Circuit (REMIC) fabricated in a 28 nm CMOS process. The chip operates in a single-photon counting (SPC) mode and contains 100 pixels with a size of 50 μm × 50 μm. It is designed for precise energy measurements using asynchronous analogue-to-digital conversion. The proposed architecture allows both fast signal processing and precise energy measurement of incoming photons to be performed independently in each pixel, occupying a small pixel area. The integrated circuit (IC) has dimensions of 1.1 mm × 1.1 mm and is currently undergoing preliminary measurements. The paper focuses on the methodology used to mitigate process variations in each of the recording channels.

Multichannel integrated circuit for time-based measurements in 28 nm CMOS

This paper discusses the application-specific integrated circuit prototype dedicated to readout of hybrid pixel X-ray detectors. The circuit is fabricated in 28 nm CMOS technology and occupies 1.1 × 1.1 mm2 of silicon area. Each of 8 × 4 pixels present in the prototype includes an analog front-end and a digital block with two ring oscillators and their supporting circuits. The circuit can operate in single-photon counting mode or time-based measurement mode. The paper discusses in detail the design decisions that influenced the final in-pixel ring oscillator architecture and layout. Measurement results are presented which demonstrate the performance of ring oscillators as well as regular operating modes of the chip: single photon counting and time-over-threshold measurement.

System for the fast readout and tests of pixel IC operating in single photon counting mode using PCIe-based FPGA

Hybrid Pixel Detectors (HPDs) have become popular in particle and photon detection techniques in recent years. This type of devices consists of two parts: a pixelated sensor (based on Si, Ge, GaAs, CZT, etc.), and a readout Integrated Circuit (IC), which usually contains thousands of pixels and millions of transistors. ICs suffer from the inaccuracies of manufacturing processes, therefore HPDs have to be thoroughly tested before the sensor bump-bonding process. This paper presents a highly efficient system for the automated testing of pixelated HPDs. The presented solution is based on the Intel Arria 10 GX Field Programmable Gate Array (FPGA) development kit and a Linux-powered Personal Computer (PC), connected via Peripheral Component Interconnect Express (PCIe) 8x Gen. 3 interface. The proposed system has been built of well-thought-out modules connected through the set of precisely defined interconnects. This approach enabled the development of an architecture that may be easily implemented in both PCIe-based systems and System-on-Chip devices, such as Intel Agilex SoC. The presented system has been tested with both a manufactured IC and a model implemented in the FPGA.

Combined fluorescence lifetime and surface topographical imaging of biological tissue.

In this work a combined fluorescence lifetime and surface topographical imaging system is demonstrated. Based around a 126 × 192 time resolved single photon avalanche diode (SPAD) array operating in time correlated single-photon counting (TCSPC) mode, both the fluorescence lifetime and time of flight (ToF) can be calculated on a pixel by pixel basis. Initial tests on fluorescent samples show it is able to provide 4 mm resolution in distance and 0.4 ns resolution in lifetime. This combined modality has potential biomedical applications such as surgical guidance, endoscopy, and diagnostic imaging. The system is demonstrated on both ovine and human pulmonary tissue samples, where it offers excellent fluorescence lifetime contrast whilst also giving a measure of the distance to the sample surface.

Photon-counting with single stoichiometric TiN layer-based optical MKIDs

We demonstrate the single photon counting mode at 405 and 850 nm with stoichiometric TiN-based microwave kinetic inductance detectors realized on a sapphire substrate and operated at bath temperatures over 300 mK. The detectors use single 15–25 nm-thick TiN layers featuring a critical temperature in the 2–3 K range. We found that the energy-resolving power R=E/ΔE exhibits an optimum with bath temperature, occurring in the 300–450 mK range, which can be almost double compared to those obtained at the lowest temperatures. Furthermore, the single photon regime is observed up to 700 mK. In addition to a high-temperature operation, the single stoichiometric layer would allow achieving a better uniformity in the critical temperature and, thus, kinetic inductance, compared to the often desired ∼1 K sub-stoichiometric TiN.

Charge sharing simulations and measurements for digital algorithms aiming at subpixel resolution in photon counting pixel detectors

Hybrid pixel detectors are segmented devices used for X-ray detection that consist of a sensor attached to the readout electronics. Detectors working in single-photon counting mode process each incoming photon individually, have essentially infinite dynamic range, and by applying energy discrimination they provide noiseless imaging. To improve the resolution of the detector and allow operation with high-intensity photon fluxes, the pixel size is reduced. However, with decreasing pixel size, a charge sharing effect is more prominent. This leads to false event registration or omitting the event, and degradation of the energy resolution of the detector. Algorithms aiming at reducing the influence of charge sharing have already been implemented on-chip. However, the spatial resolution of the detector can be increased beyond the physical size of the pixel if the charge proportions collected by neighboring pixels are analyzed.The simulations show that charge cloud size referred to pixel size and noise are the key parameters that determine the accuracy of the subpixel algorithm. The article shows the concept of subpixel algorithm and the simulations for different detector parameters and approximation algorithms. The slanted-edge method was implemented to quantify the resolution of detectors consisting standard readout architecture. The chips were simulated and tested to verify the influence of different bias voltages, sensor materials, and thicknesses on charge sharing and as a consequence on the detector resolution. The simulated and measured edge spread functions were compared. The results show that the simulator can be used to describe the spatial resolution of the detectors, and can be used for further studies of the resolution of detectors with subpixel algorithm implemented.

Small pixel high-spatial resolution photon-counting prototype IC for synchrotron applications

This paper presents the design and simulation of a prototype chip in the CMOS 40 nm process for high spatial resolution operation at the ESRF-EBS synchrotron. The core of the prototype IC is the pixel matrix with 50 µm pitch, operating in a single photon counting mode. Each pixel contains a Charge Sensitive Amplifier (CSA) with a fast discharge block and detector leakage current compensation circuit. The CSA output is directly connected to the discriminator with an offset trimming capability. The chip is optimized for operation with a monochromatic X-ray beam with an energy of up to 30 keV. Furthermore, several algorithms of interpixel communication are implemented in the chip to increase detector spatial resolution by using the charge sharing effect.

A prototype pixel readout chip working in single photon counting mode with a novel charge sharing suppression scheme

Spectral distortion due to the charge sharing effect becomes a severe issue in single-photon counting pixel detectors. The HEPS-BPIX4 prototype chip, dedicated for the HEPS in China, implements a novel architecture to mitigate charge sharing and permit spectroscopic imaging with high efficiency. In the architecture, a central pixel communicates with others in a cluster of 3 × 3 pixels. The algorithm simulation showed a charge sharing elimination accuracy better than 90%. The prototype chip has been designed in a 130 nm CMOS technology. The preliminary measurements show a charge gain of 48 mV/ke− and an equivalent noise charge of 150 e− rms. Detailed tests in a 4 × 4 pixel array for the charge sharing are performed using electrical test pulses. The hit allocation in the core four adjacent pixels of the array indicates that effective suppression of charge sharing has been realized.

Room-Temperature Persistent Luminescence in Metal Halide Perovskite Nanocrystals for Solar-Driven CO 2 Bioreduction

Room-Temperature Persistent Luminescence in Metal Halide Perovskite Nanocrystals for Solar-Driven CO ₂ Bioreduction

Spectrum1k — integrated circuit for medical imaging designed in CMOS 40 nm

We present a multichannel integrated circuit of pixel architecture designed in CMOS 40 nm technology. The chip is composed of 40 × 24 pixels of 75 µm pitch working in the single photon counting mode, each built of front-end amplifier, peak and hold detector, 6-bit analog to digital converter, and memory composed of 64 × 12-bit counters. Thanks to the proposed functionality it is possible to store in each pixel separately information of incoming particles energy spectrum. The chip is dedicated to operating with both electrons and holes of 2.2 ke−–35 ke− energy range. The IC occupies an area of 2 × 4.5 mm2, is already back from fabrication, and is under preliminary measurements.

Pixel readout IC for CdTe detectors operating in single photon counting mode with interpixel communication

This paper presents a readout integrated circuit (IC) of pixel architecture called MPIX (Multithreshold PIXels), designed for CdTe pixel detectors used in X-ray imaging applications. The MPIX IC area is 9.6 mm × 20.3 mm and it is designed in a CMOS 130 nm process. The IC core is a matrix of 96 × 192 square-shaped pixels of 100 µm pitch. Each pixel contains a fast analog front-end followed by four independently working discriminators and four 12-bit ripple counters. Such pixel architecture allows photon processing one by one and selecting the X-ray photons according to their energy (X-ray colour imaging). To fit the different range of applications the MPIX IC has 8 possible different gain settings, and it can process the X-ray photons of energy up to 154 keV. The MPIX chip is bump-bonded to the CdTe 1.5 mm thick pixel sensor with a pixel pitch of 100 µm. To deal with the charge sharing effect coming from a thick semiconductor pixel sensor, multithreshold pattern recognition algorithm is implemented in the readout IC. The implemented algorithm operates both in the analog domain (to recover the total charge spread between neighboring pixels, when a single X-ray photon hits the border of the pixel) and in the digital domain (to allocate a hit position to a single pixel).

Measurements of charge sharing in a hybrid pixel photon counting CdTe detector

Hybrid pixel radiation detectors working in a single-photon counting mode have gained increasing attention due to their noiseless imaging and high dynamic range. Due to the fact that sensors of different materials can be attached to the readout circuit, they allow operation with a wide range of photon energies. The performance of the single photon counting detectors is limited by pile-up. To allow a detector to work under high flux conditions, the pixel size is reduced, which minimizes detector dead time. However, with smaller pixel sizes the charge sharing effect, a phenomenon that deteriorates both detection efficiency and spatial resolution is more profound.The influence of charge sharing on the detector performance can be quantified using parameterization of the s-curve obtained in the spectral response measurements. The article presents the measurements of the response function of a hybrid pixelated photon counting detector for certain primary energy, which corresponds to the probability of detecting a photon as a function of its energy deposition. The measurements were carried out using an X-ray tube by performing a threshold scan during illumination with X-ray photons of a 1.5 mm and 0.75 mm thick CdTe detector with 100 µm pixel pitch. The charge size cloud depends on the sensor material, the bias voltage, and the sensor thickness. Therefore, the experimental data from a sensor biased with different bias voltages are compared to the theoretical results based on a cascaded model of a single-photon counting segmented silicon detector. The study of the charge sharing influence on the spatial resolution of the CdTe detector will serve for a further study of the possible implementations of the algorithms achieving subpixel resolution, in which the charge sharing becomes the desired effect since the charge division in the pixels is used to interpolate the photon interaction position.

Vernier time-to-digital converter with ring oscillators for in-pixel time-of-arrival and time-over-threshold measurement in 28 nm CMOS

The paper describes a design of a prototype chip in 28 nm CMOS technology, consisting of 8 × 4 pixels with 50 μm pitch, dedicated for the precise measurement of Time-of-Arrival (ToA) and Time-over-Threshold (ToT) with a resolution within the picosecond range. To address this requirement, in-pixel Vernier time-to-digital converter (TDC) has been implemented, which utilizes two ring oscillators per pixel. Overall chip architecture is introduced as well as pixel architecture and selected simulation results. The pixel consists of a recording channel and TDC part. The recording channel is composed of an inverter-based front-end amplifier with Zimmerman feedback, a discriminator, a calibration block and a threshold setting block. TDC part includes two ring oscillators together with their calibration blocks and additional logic with counters/shift registers that allow for precise ToA measurement (using Vernier method) as well as ToT measurement (using one of the oscillators). Alternatively, single photon counting (SPC) mode can be used. Frequency of oscillators is set in three steps. First, two global 8-bit digital-to-analog converters (DACs) are used for initial setting of all ring oscillators. Then, per-oscillator capacitance bank and 6-bit DAC are used for fine setting. Simulation results of core blocks suggest that the ToA resolution on the order of tens of picoseconds may be achieved. The chips are already fabricated and are currently being prepared for measurements.

Self-assembly of semiconductor quantum dots with porphyrin chromophores: Energy relaxation processes and biomedical applications

A “bottom-up” self-assembly strategy was used for the directed formation of two types of heterogeneous organic-inorganic nanoassemblies based on colloidal semiconductor quantum dots (QDs) and porphyrin molecules: (i) TOPO-capped CdSe/ZnS core/shell QDs attached via coordination interactions with tetra-pyridylporphyrins, H2P(3′-Py)4, in toluene, and (ii) AgInS/ZnS core/shell QDs stabilized by glutathione (GSH) electrostatically coupled with positively charged porphyrin molecules H2P(4′-MePy+)4 via Coulomb attraction in water. Using a quantitative experimental analysis of the QD photoluminescence quenching in QD-porphyrin nanoassemblies (steady-state, time-resolved, time correlated single photon counting mode (TCSPC) spectroscopy) as well as theoretical calculations and quantum chemical modeling, it is shown that upon attachment of porphyrin molecules to QDs surface-mediated processes dictate the probability of several competing non-radiative photophysical phenomena leading to static and dynamic quenching of the QD photoluminescence: (i) non-radiative energy transfer QD→porphyrin of Foerster type; (ii) non-FRET processes including electron tunneling beyond the QD core under conditions of quantum confinement; (iii) the influence of the dynamics of capping ligand molecules leading to the formation of near band edge states (surface traps). The competition between FRET and non-FRET quenching processes drastically depends on the QD size as well as the solvent and the spatial displacement of porphyrin macrocycles on the QD surface. On the basis of the results obtained the nanoassemblies are demonstrated to be promising for various biomedical applications (drug delivery carriers, distant testing of local pH, singlet oxygen generation for the photodynamic treatment, etc.).

HEPS-BPIX3: a fine pitch pixel readout chip working in single photon counting mode for synchrotron radiation applications

HEPS-BPIX3 is a hybrid pixel detector readout chip for X-ray applications for the High Energy Photon Source (HEPS) in China. The readout chip contains an array of 88 × 88 pixels with a pixel size of 55 μm × 55 μm, working in single photon counting mode. Each pixel handles both polarities of positive and negative input charge signals and has a counting depth of 11 bits. Using a clock with a frequency up to 160 MHz, the chip can read out serially with zero dead time. Designed in a 130 nm CMOS technology, the chip has been measured and given the CSA charge gain of 17.6 mV/ke- for electron collection and 13 mV/ke- for hole collection, respectively. Bump-bonded detector modules with a 320-μm-thick silicon sensor were also tested. The test results showed an equivalent input noise of 156 e- and a counting rate up to 2.2 Mcps. Besides, an image using an X-ray tube was demonstrated and a frame rate of 1.8 kHz could be guaranteed. Measured characteristics present the normal functionality of the HEPS-BPIX3 chip and prove that the chip satisfies the HEPS requirements.

UVscope and its application aboard the ASTRI-Horn telescope

UVscope is an instrument, based on a multi-pixel photon detector, developed to support experimental activities for high-energy astrophysics and cosmic ray research. The instrument, working in single photon counting mode, is designed to directly measure light flux in the wavelengths range 300-650 nm. The instrument can be used in a wide field of applications where the knowledge of the nocturnal environmental luminosity is required. Currently, one UVscope instrument is allocated onto the external structure of the ASTRI-Horn Cherenkov telescope devoted to the gamma-ray astronomy at very high energies. Being co-aligned with the ASTRI-Horn camera axis, UVscope can measure the diffuse emission of the night sky background simultaneously with the ASTRI-Horn camera, without any interference with the main telescope data taking procedures. UVscope is properly calibrated and it is used as an independent reference instrument for test and diagnostic of the novel ASTRI-Horn telescope.

The time-resolved hard X-ray diffraction endstation KMC-3 XPP at BESSY II.

The time-resolved hard X-ray diffraction endstation KMC-3 XPP for optical pump/X-ray probe experiments at the electron storage ring BESSY II is dedicated to investigating the structural response of thin film samples and heterostructures after their excitation with ultrashort laser pulses and/or electric field pulses. It enables experiments with access to symmetric and asymmetric Bragg reflections via a four-circle diffractometer and it is possible to keep the sample in high vacuum and vary the sample temperature between ∼15 K and 350 K. The femtosecond laser system permanently installed at the beamline allows for optical excitation of the sample at 1028 nm. A non-linear optical setup enables the sample excitation also at 514 nm and 343 nm. A time-resolution of 17 ps is achieved with the `low-α' operation mode of the storage ring and an electronic variation of the delay between optical pump and hard X-ray probe pulse conveniently accesses picosecond to microsecond timescales. Direct time-resolved detection of the diffracted hard X-ray synchrotron pulses use a gated area pixel detector or a fast point detector in single photon counting mode. The range of experiments that are reliably conducted at the endstation and that detect structural dynamics of samples excited by laser pulses or electric fields arepresented.

Equipment design and performance characterization of full field x-ray fluorescence (FF-XRF) element distribution imaging system with combined collimating lens (CCL).

This work describes a full field x-ray fluorescence element distribution imaging system with a combined collimating lens (CCL), which is more suitable for a higher x-ray energy range (12 keV-30 keV). The system consists of an optical-use charge-coupled device (CCD) camera coupled to a combined collimating lens (CCL), which includes pinhole collimator and x-ray window, x-ray tube, and sample room. The continuously variable magnification of 0.5-2 is achieved under a compact structure. The x-ray spectrum and two-dimensional element distribution mapping of the irradiated sample are obtained by processing a series of images acquired by using the CCD camera in a single photon counting mode. The energy resolution is 275 eV at the reference energy of 14.957 keV (yttrium Kα, Z = 39). The limit of detection is 46.41 ppm by measuring yttrium standard solution. The spatial resolution is 135 μm when using a 100 μm pinhole at the magnification of 1. Samples made by metal foils and mineral pigments are tested, and the results proved that the system was reliable when detecting elements of a high atomic number.