Crosstalk Probability Research Articles

Characterization of a SiPM-based monolithic neutron scatter camera using dark counts

The Single Volume Scatter Camera (SVSC) Collaboration aims to develop portable neutron imaging systems for a variety of applications in nuclear non-proliferation. Conventional double-scatter neutron imagers are composed of several separate detector volumes organized in at least two planes. A neutron must scatter in two of these detector volumes for its initial trajectory to be reconstructed. As such, these systems typically have a large footprint and poor geometric efficiency. We report on the design and characterization of a prototype monolithic neutron scatter camera that is intended to significantly improve upon the geometrical shortcomings of conventional neutron cameras. The detector consists of a 50 mm×56 mm× 60 mm monolithic block of EJ-204 plastic scintillator instrumented on two faces with arrays of 64 Hamamatsu S13360-6075PE silicon photomultipliers (SiPMs). The electronic crosstalk is limited to < 5% between adjacent channels and < 0.1% between all other channel pairs. SiPMs introduce a significantly elevated dark count rate over PMTs, as well as correlated noise from after-pulsing and optical crosstalk. In this article, we characterize the dark count rate and optical crosstalk and present a modified event reconstruction likelihood function that accounts for them. We find that the average dark count rate per SiPM is 4.3 MHz with a standard deviation of 1.5 MHz among devices. The analysis method we employ to measure internal optical crosstalk also naturally yields the mean and width of the single-electron pulse height. We calculate separate contributions to the width of the single-electron pulse-height from electronic noise and avalanche fluctuations. We demonstrate a timing resolution for a single-photon pulse to be (128 ± 4) ps. Finally, coincidence analysis is employed to measure external (pixel-to-pixel) optical crosstalk. We present a map of the average external crosstalk probability between 2×4 groups of SiPMs, as well as the in-situ timing characteristics extracted from the coincidence analysis. Further work is needed to characterize the performance of the camera at reconstructing single- and double-site interactions, as well as image reconstruction.

Characterization of external optical crosstalk reduction for SiPM-based scintillation detectors with an optical bandpass filter

External optical crosstalk remains a significant source of correlated noise in scintillation detectors optically coupled to silicon photomultiplier (SiPM) arrays and can influence achievable performance by limiting the maximum overvoltage at which a detector can be operated. This study evaluated the potential benefits of incorporating an optical bandpass filter, which is absorptive to optical crosstalk and transmissive for scintillation photons, between the scintillator and SiPM array. Several SiPM and bandpass configurations were characterized, including single-element and SiPM arrays with bare, filter-coupled, crystal-coupled, and crystal-filter-coupled interfaces. Coupling the optical filter between a 4 × 4 array of Broadcom AFBR-S4N44P164 M (NUV-MT) SiPMs and a 12 × 12 × 20 mm3 LYSO crystal decreased the total number of detected optical photon noise by up to 92%. The impact of the filter on crosstalk probability reduction was also characterized by the single-channel measurements with the same SiPM, suppressing external crosstalk up to 64%. With the filter coupled, SiPMs were operable at very high overvoltage. The results of these studies demonstrate that optical filtering is a promising technique to significantly reduce correlated noise in scintillation detectors employing SiPMs.

A novel measurement method for SiPM external crosstalk probability at low temperature

A novel measurement method for SiPM external crosstalk probability at low temperature

A 3.06 μm Single-Photon Avalanche Diode Pixel with Embedded Metal Contact and Power Grid on Deep Trench Pixel Isolation for High-Resolution Photon Counting.

In this study, a 3.06 μm pitch single-photon avalanche diode (SPAD) pixel with an embedded metal contact and power grid on two-step deep trench isolation in the pixel is presented. The embedded metal contact can suppress edge breakdown and reduce the dark count rate to 15.8 cps with the optimized potential design. The embedded metal for the contact is also used as an optical shield and a low crosstalk probability of 0.4% is achieved, while the photon detection efficiency is as high as 57%. In addition, the integration of a power grid and the polysilicon resistor on SPAD pixels can help to reduce the voltage drop in anode power supply and reduce the power consumption with SPAD multiplication, respectively, in a large SPAD pixel array for a high-resolution photon-counting image sensor.

Modulation in gene expression and enzyme activity suggested the roles of monodehydroascorbate reductase in development and stress response in bread wheat

Monodehydroascorbate reductase (MDHAR) is a crucial enzymatic antioxidant of the ascorbate-glutathione pathway involved in reactive oxygen species scavenging. Herein, we identified 15 TaMDHAR genes in bread wheat. Phylogenetic analysis revealed their clustering into three groups, which are also related to the subcellular localization in the peroxisome matrix, peroxisome membrane, and chloroplast. Each TaMDHAR protein consisted of two conserved domains; Pyr_redox and Pyr_redox_2 of the pyridine nucleotide disulfide oxidoreductase family. The occurrence of diverse groups of cis-regulatory elements in the promoter region and their interaction with numerous transcription factors suggest assorted functions of TaMDHARs in growth and development and in light, phytohormones, and stress responses. Expression analysis in various tissues further revealed their importance in vegetative and reproductive development. In addition, the differential gene expression and enhanced enzyme activity during drought, heat, and salt treatments exposed their role in abiotic stress response. Interaction of MDHARs with various antioxidant enzymes and biochemicals related to the ascorbate-glutathione cycle exposed their synchronized functioning. Interaction with auxin indicated the probability of cross-talk between antioxidants and auxin signaling. The miR168a, miR169, miR172 and others interaction with various TaMDHARs further directed their association with developmental processes and stress responses. The current study provides extensive information about the importance of TaMDHARs, moreover, the precise role of each gene needs to be established in future studies.

CALIBRATION OF 122 SENSL MICROFJ-60035 SIPMS AND THE REDUCTION OF OPTICAL CROSS-TALK DUE TO COUPLED LIGHT GUIDES

Recent silicon photomultipliers (SiPMs) boast excellent production quality, eliminating the need for individual breakdown voltage calibration. We present measurements of cross-talk probability and relative gain for 122 SensL MicroFJ-60035-TSV SiPMs. These semiconductor photosensors have replaced photomultiplier tubes in many applications due to their single-photon resolution, insensitivity to magnetic fields, robustness, and cost-effective photon detection at lower voltages. Light guides expand SiPMs' small photosensitive area, and optical coupling reduces cross-talk probability compared to bare sensors at nominal bias voltage, as demonstrated in this study.

Characterization of Hamamatsu S13161-3050AE-08 SiPM (8 × 8) array at different temperatures with CAEN DT5202

Silicon PhotoMultipliers, SiPMs, constitute the enabling technology for a diverse and rapidly growing range of applications: medical imaging, experimental physics, and commercial applications are only a few examples. In this work, a characterization protocol for SiPM qualification has been applied to Hamamatsu S13161-3050AE-08 SiPM (8 × 8) array in the (−40 ÷ ＋30) °C temperature range. The protocol foresees to measure several parameters: breakdown voltage, quenching resistance, gain, dark count rate and probability of cross-talk. Methods to extract them and their dependence on temperature at fixed overvoltage are shown and the results are discussed.

Average capacity of an underwater wireless communication link with the quasi-Airy hypergeometric-Gaussian vortex beam based on a modified channel model.

Prompted by alleviating the random perturbation of underwater channel and enhancing the performance for the orbital angular momentum (OAM) -based underwater wireless optical communication (UWOC), the quasi-Airy Hypergeometric-Gaussian (QAHyGG) vortex beam is first proposed and demonstrated. Moreover, an underwater channel model is first modified for more accurate simulated results of the propagation property of various beams. Based on the modified model, the transmission and communication performance of three different OAM-carrying beams (the Gauss vortex (GV) beam, the Hypergeometric-Gaussian (HyGG) vortex beam, and the QAHyGG vortex beam) are comparatively studied. In addition, the parameters optimization of the QAHyGG vortex beam is made for further enhancing the average capacity. The results show that the QAHyGG vortex beam exhibits higher received power and lower crosstalk probability under different channel conditions. The average capacity of the QAHyGG vortex beam has enhanced by ∼8% and ∼27% compared with the HyGG vortex beam and the GV beam at 100m, respectively. The QAHyGG vortex beam is more suitable in an OAM-based UWOC system with a limited-size receiving aperture or lower transmit power. Besides, the average capacity will improve effectively at longer distances with the optimized beam parameters. These research results can provide advances in designing the practical OAM-based UWOC system.

Anisotropic plasma sheath turbulence effects on the mode states of Whittaker–Gaussian beams

In this paper detection probability and crosstalk probability variance of the orbital angular momentum states of the diffraction-free Whittaker–Gaussian (WG) beams passing through an anisotropic plasma sheath turbulence (PST) are theoretically formulated. In this regard, using modified von Karman spectrum in the frame of Rytov theory the spiral spectrum of the WG beams is derived, and the role of the anisotropy parameters, refractive index fluctuation variance, initial topological charge, receiving aperture radius, the outer scale of turbulence, beam wavelength and waist in the mitigation of the turbulence-induced disturbance is numerically explored. The remarkable findings indicate that WG beams in anisotropic PST are less influenced than isotropic one, and increasing the anisotropy feature of plasma medium leads to alleviate modulated distortion. Furthermore, it is found out that the propagation performance of WG vortex beams with high-order initial topological charge is significantly better than those with lower order. We expect that our results will be helpful for designing optimal free-space communication systems.

DCR and crosstalk characterization of a bi-layered 24 × 72 CMOS SPAD array for charged particle detection

This paper presents the results from the crosstalk and dark count rate (DCR) characterization of a 24 × 72 single photon avalanche diode (SPAD) array, fabricated in a 150 nm CMOS technology. The chip under test consists of a dual layer detection system developed in view of applications to charged particle tracking. A three step procedure, used for the crosstalk characterization, is presented. The crosstalk probability, taking place in 5 × 5 sub arrays built around noisy pixels, has been computed. Eventually, random telegraph signal (RTS) fluctuations in DCR, at different bias conditions, are briefly discussed.

Direct detection of charged particles with SiPMs

The direct response of Silicon PhotoMultipliers being traversed by a MIP charged particle have been studied in a systematic way for the first time. Using beam test data, time resolution and the crosstalk probability have been measured. A characterization of the SiPM by means of a laser beam is also reported. The results obtained for different sensors indicate a measured time resolution around 40–70 ps. Although particles are expected to traverse only one SPAD per event, crosstalk measurements on different sensors indicate an unexpected higher value with respect to the one related to the sensor noise.

Design and Analysis of a Photon Counting System Using Covered Single-Photon Avalanche Photodiode

A photon counting system using covered single-photon avalanche diode (SPAD) based on a standard integrated circuit (IC) process ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.18~\mu \text{m}$ </tex-math></inline-formula> ) is designed and analyzed in this work. The SPAD is formed using the medium voltage (MV) doping layers of the process. To reduce the dark count rate (DCR) in the SPAD, a shaded SPAD with the same structure is fabricated on the same chip which is covered by a metal layer and only providing DCR for the DCR correction. This DCR provided by the shaded SPAD can also be used for the real time on chip monitoring of some other parameters, such as temperature, breakdown voltage, and afterpulsing probability. Experimental results show that the SPAD developed is able to detect the visible light from 450 to 850 nm with a 35% peak photon detection probability (PDP) achieved at around 550 nm with a bias voltage of 16 V (excess voltage of 3 V). A timing jitter of 176 ps is measured with an excess voltage of 3 V. The DCR in the SPAD tested is about 1.38 cps/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}^{2}$ </tex-math></inline-formula> with an excess bias voltage of 1 V and 14.62 cps/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}^{2}$ </tex-math></inline-formula> with the excess bias voltage of 3 V without the DCR correction. Results also show that a reduction of more than 85% in the DCR (background noise) can be achieved when the DCR correction is applied resulting in a DCR of 1.68 cps/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}^{2}$ </tex-math></inline-formula> with an excess bias voltage of 3 V. By monitoring the DCR of the shaded SPAD, the breakdown voltage and temperature of other on chip SPAD can be measured. The potential usefulness of the afterpulsing probability monitoring using the shaded SPAD and the crosstalk probability (CTP) between SPADs on the chip are analyzed. In addition, the effects of process variations on the SPAD performance are investigated by testing ten chips with the same SPADs fabricated, and a potential method is proposed for alleviate the process variations in the SPAD arrays.

Probability of orbital angular momentum for square Hermite–Gaussian vortex pulsed beam in oceanic turbulence channel

By the theory of localized waves and the vectorial solution of the Maxwell equation, we develop and explore the vector characteristics of the new square Hermite–Gaussian vortex pulsed beam possessing orbital angular momentum (OAM). To investigate the propagation performance of this new beam, the measurement probability model of OAM states for square Hermite–Gaussian vortex pulsed beam propagation through oceanic turbulence is built. We discover through the numerical simulation that a large propagation distance causes a large delay of arrival time for this vortex pulsed beam. Under the same conditions, both the measurement signal probability and the measurement crosstalk probability of OAM states reach the peak at the arrival time. The wide initial half-pulse width and the low OAM quantum number can improve a measurement signal probability and decrease a measurement crosstalk probability of OAM states. Oceanic turbulence with a weak dissipation rate of mean-squared temperature, a small temperature and salinity ratio, a long inner scale and a strong dissipation rate of turbulent kinetic energy has a weak disturbance on the measurement signal probability and a strong disturbance on the measurement crosstalk probability of OAM states for the square Hermite–Gaussian vortex pulsed beam.

Spiral spectrum of high-order elliptic Gaussian vortex beams in a non-Kolmogorov turbulent atmosphere.

In a free space optical communication system based on vortex beams, the effects of spread and crosstalk caused by atmospheric turbulence should not be ignored. The orbital angular momentum (OAM) spectrum of the signal based on elliptic Gaussian beam (EGB) after propagation through non-Kolmogorov turbulent atmosphere are deduced, and a theoretical model of the spiral spectrum of EGB propagating through turbulent atmosphere is obtained. Numerically calculated OAM modes detection and crosstalk probability under different ellipticity parameters. The results show that the ellipticity parameter has a significant impact on the OAM spectral distribution of EGB and the transmission characteristics after turbulent atmosphere. The selection of appropriate ellipticity parameter can correspondingly reduce the degradation and crosstalk caused by turbulent atmosphere. We also compared a Laguerre-Gaussian beam (LGB) with EGB and pointed out the advantages and limitations of these two kinds of beams. The research results may be useful in the field of short distance optical communication and OAM-based multiplex communication.

Optical crosstalk photon penetration depth in Silicon Photomultipliers

In recent years, many researchers have explored the application of Silicon Photomultipliers (SiPMs) in various weak light detection fields. Optical crosstalk probability (Pct) is one of the most important parameters of the SiPM, so the performance of the device may be optimized by further research on the Pct mechanism. The two-dimensional (2D) and 1D spatial distribution analysis of optical crosstalk probability in a typical SiPM were employed in this study via pulsed laser focusing and precision displacement methods in order to obtain the penetration depth of optical crosstalk photons in the SiPM. It was believed that there are five propagating modes of crosstalk photons in SiPM. One of the propagating modes is that the crosstalk photons generated by an avalanche photodiode (APD) cell passing through the substrate material and reflecting to other APD cells at the bottom interface of the substrate, thus causing other APD cells to avalanche. However, the probability of this crosstalk photon propagating mode appears to be negligible. By fitting the experimental results, the penetration depth of crosstalk photons in the SiPM was determined to be less than 22 micrometers. As the substrate thickness of most SiPMs is more than 300 micrometers, the probability of crosstalk photons passing through SiPM substrate material and reflecting to other APD is less than 1.4 E-12. Therefore, this crosstalk mode needs not be considered in the crosstalk mechanism analysis of SiPMs. A novel technique for measuring the effective propagating distance of the crosstalk photons in SiPMs was developed which can be used to characterize the effective action distance of the crosstalk photons in different structures and types of SiPMs. This work may provide a reference for the design and fabrication of SiPMs in the future.

Discrete probabilistic detection model for a Geiger-mode avalanche photodiode array with crosstalk.

A discrete-time probability model is proposed to predict the detection performance of the Geiger-mode avalanche photodiode array. This model is established by considering multiple influencing factors, and crosstalk is characterized in the form of a transition matrix during the modeling process. The verification experiment shows that the results are consistent with previous results for a crosstalk-free scenario. The performance analysis also indicates that the array detection performance decreases approximately linearly with the increase of crosstalk probability. When the crosstalk probability is 20%, compared with the scenario without considering crosstalk effects, the deviation of array detection probability reaches up to 27.05%.

Quantum detector tomography of a 2×2 multi-pixel array of superconducting nanowire single photon detectors.

We demonstrate quantum detector tomography of a commercial 2×2 array of superconducting nanowire single photon detectors. We show that detector-specific figures of merit including efficiency, dark-count and cross-talk probabilities can be directly extracted, without recourse to the underlying detector physics. These figures of merit are directly identified from just four elements of the reconstructed positive operator valued measure (POVM) of the device. We show that the values for efficiency and dark-count probability extracted by detector tomography show excellent agreement with independent measurements of these quantities, and we provide an intuitive operational definition for cross-talk probability. Finally, we show that parameters required for the reconstruction must be carefully chosen to avoid oversmoothing the data.

Local Efficacy of Glutamate Uptake Decreases with Synapse Size

Synaptically released glutamate is largely cleared by glutamate transporters localized on perisynaptic astrocyte processes. Therefore, the substantial variability of astrocyte coverage of individual hippocampal synapses implies that the efficacy of local glutamate uptake and thus the spatial fidelity of synaptic transmission is synapse dependent. By visualization of sub-diffraction-limit perisynaptic astrocytic processes and adjacent postsynaptic spines, we show that, relative to their size, small spines display a stronger coverage by astroglial transporters than bigger neighboring spines. Similarly, glutamate transients evoked by synaptic stimulation are more sensitive to pharmacological inhibition of glutamate uptake at smaller spines, whose high-affinity N-methyl-D-aspartate receptors (NMDARs) are better shielded from remotely released glutamate. At small spines, glutamate-induced and NMDAR-dependent Ca2+ entry is also more strongly increased by uptake inhibition. These findings indicate that spine size inversely correlates with the efficacy of local glutamate uptake and thereby likely determines the probability of synaptic crosstalk.

Superresolution Limits from Measurement Crosstalk.

Superresolution techniques based on intensity measurements after a spatial mode decomposition can overcome the precision of diffraction-limited direct imaging. However, realistic measurement devices always introduce finite crosstalk in any such mode decomposition. Here, we show that any nonzero crosstalk leads to a breakdown of superresolution when the number N of detected photons is large. Combining statistical and analytical tools, we obtain the scaling of the precision limits for weak, generic crosstalk from a device-independent model as a function of the crosstalk probability and N. The scaling of the smallest distance that can be distinguished from noise changes from N^{-1/2} for an ideal measurement to N^{-1/4} in the presence of crosstalk.

Comparative Study of Spiral Spectrum of Elegant and Standard Laguerre–Gaussian Beams in Atmospheric Turbulence

We derive the analytical expression of the probability density of orbital angular momentum modes for elegant and standard Laguerre–Gaussian beams in turbulence. The results show that we can increase the initial topological charge of the beams to reduce the detrimental mode crosstalk induced by the turbulence. We also discuss the influence of the beam parameters on the probability of signal and the variances of crosstalk probability. The results obtained show that the beams with smaller beam width and longer wavelength have higher detection probabilities of signal and are less affected by turbulence. Comparing with the results of elegant and standard Laguerre–Gaussian beams, we find that elegant Laguerre–Gaussian beams display stronger turbulence resistance. Our results will be useful in free-space optical communications.