High Photon Count Rates Research Articles

A novel spaceborne photon-counting laser altimeter denoising method based on parameter-adaptive density clustering

ABSTRACT To tackle the challenge of denoising spaceborne photon-counting laser altimeter point clouds with uneven noise density, this study proposes a denoising method based on adaptive parameter density clustering, which utilizes numerical simulations to achieve self-adaptation of key parameters (neighborhood radius Eps and minimum number of points MinPts ). First, taking the directional adaptive ellipse DBSCAN (DAE-DBSCAN) as an example, photons with different background photon count rates ( bckgrd _ rate ) are used to traverse Eps and MinPts to calculate their optimal values ( Eps and MinPts with the highest denoising accuracy). Then, a mathematical prediction model of bckgrd _ rate , Eps and MinPts was established. The actual background photon count rates were introduced into the key parameter prediction model to obtain the optimal Eps and MinPts . Finally, a denoising experiment was conducted using the simulated photons and the ATLAS data. The results show that the proposed method had higher accuracy than the constant parameter denoising method, with an F >0.95. Even for photons of complex mountainous terrain with a high background photon count rate, the denoising accuracy was still higher than 0.9. The proposed method improves the denoising accuracy of photons with different noise densities by adapting density clustering parameters.

A compact multi-pixel superconducting nanowire single-photon detector array supporting gigabit space-to-ground communications.

Classical and quantum space-to-ground communications necessitate highly sensitive receivers capable of extracting information from modulated photons to extend the communication distance from near-earth orbits to deep space explorations. To achieve gigabit data rates while mitigating strong background noise photons and beam drift in a highly attenuated free-space channel, a comprehensive design of a multi-functional detector is indispensable. In this study, we present an innovative compact multi-pixel superconducting nanowire single-photon detector array that integrates near-unity detection efficiency (91.6%), high photon counting rate (1.61 Gcps), large dynamic range for resolving different photon numbers (1-24), and four-quadrant position sensing function all within one device. Furthermore, we have constructed a communication testbed to validate the advantages offered by such an architecture. Through 8-PPM (pulse position modulation) format communication experiments, we have achieved an impressive maximum data rate of 1.5 Gbps, demonstrating sensitivities surpassing previous benchmarks at respective speeds. By incorporating photon number information into error correction codes, the receiver can tolerate maximum background noise levels equivalent to 0.8 photons/slot at a data rate of 120 Mbps-showcasing a great potential for daylight operation scenarios. Additionally, preliminary beam tracking tests were conducted through open-loop scanning techniques, which revealed clear quantitative dependence indicating sensitivity variations based on beam location. Based on the device characterizations and communication results, we anticipate that this device architecture, along with its corresponding signal processing and coding techniques, will be applicable in future space-to-ground communication tasks.

A Photon Imaging Detector Model with High Resolution and High Counting Rate

A cross strip (XS) anode detector is a photon-counting imaging detector with high spatial resolution. However, due to the Poisson distribution characteristics of the photons emitted by the target, photons with a small time interval will cause signal superposition and resolution degradation. This is particularly significant at a high photon count rate. The key link that restricts the counting rate of the XS detector is the electronic system. In this paper, we propose a new electronic signal processing system scheme using a digital trapezoidal shaping filter instead of a traditional Gaussian shaping filter, which enables the detector to maintain a high resolution at high count rates. In order to verify the feasibility of the scheme, the relationship between shaping errors and shaping parameters is studied. Furthermore, the relationship between spatial resolution and photon-counting rate at different noise levels is revealed by numerical simulation. The results show that the detector can achieve a spatial resolution of <50 μm at a photon count rate of >6 MHz for 1000 e RMS noise.

Improved response model of a superconducting nanowire array for high photon count rate communication

In high-speed photon-counting communication where the slot duration is close to the scale of detector reset time, the detection efficiency recovery characteristics of superconducting nanowire single photon detector (SNSPD) become the key factors affecting counting and communication performance. We introduced the nonlinear detection efficiency recovery model derived from the kinetic inductance model combined with the nonlinear efficiency-current relationship into the pulse position modulation (PPM) optical communication system based on the SNSPD array, and studied the impact of the recovery characteristics on the counting and communication performance of the system. On this basis, we introduce the efficiency recovery model into the correction of the channel logarithmic likelihood ratio (LLR) to estimate the SNR of each slot more accurately. Relevant results show that compared with the existing Poisson channel model, fixed deadtime model and detection efficiency exponential recovery model, this modification combined with FEC can provide the best decoding performance, especially in scenarios with high PPM order, small array pixel number and strong noise level. Besides, the nonlinear detection efficiency recovery model also reflects the best consistency with the experimental measurements of the SNSPD array in terms of response count rates near saturation.

Experimental characterization of a fast X-ray spectroscopic imager module using the ALTAIR P3 ASIC for real-time contaminants detection

X-ray imagers with spectroscopic capabilities and high photon count rates are finding promising applications in industrial real-time inspection systems. In this context, XSpectra® combines a CdTe-based linear energy-resolved photon counting (ERPC) pixel sensor with real-time image processing techniques to detect low and high density contaminants. The detection unit makes use of a new analog read-out ASIC that has been designed by Politecnico di Milano to meet strict application requirements both in energy resolution and achievable photon count rate. A room-temperature low-rate spectroscopic characterization of the system at a peaking time of 60 ns showed an average equivalent noise charge of 259 electrons r.m.s. (2.72 keV FWHM in CdTe) and an average FWHM of the 59.5 keV 241Am line of 3.6 keV, with a 3σ dispersion in noise performance of ±10% over 256 channels. The detection unit was tested in high incoming photon flux conditions by means of an X-ray tube. Minimal spectral distortion due to pile-up events is obtained up to an Incoming Count Rate of 2.5 Mcps/channel, while the maximum counting capability of energy-resolved events is 2.2 Mcps/channel.

Improved Response Model of a Superconducting Nanowire Array for High Photon Count Rate Communication

Improved Response Model of a Superconducting Nanowire Array for High Photon Count Rate Communication

Room-temperature coherent manipulation of single-spin qubits in silicon carbide with a high readout contrast.

Spin defects in silicon carbide (SiC) with mature wafer-scale fabrication and micro/nano-processing technologies have recently drawn considerable attention. Although room-temperature single-spin manipulation of colour centres in SiC has been demonstrated, the typically detected contrast is less than 2n}{}%, and the photon count rate is also low. Here, we present the coherent manipulation of single divacancy spins in 4H-SiC with a high readout contrast (n}{}-30%) and a high photon count rate (150 kilo counts per second) under ambient conditions, which are competitive with the nitrogen-vacancy centres in diamond. Coupling between a single defect spin and a nearby nuclear spin is also observed. We further provide a theoretical explanation for the high readout contrast by analysing the defect levels and decay paths. Since the high readout contrast is of utmost importance in many applications of quantum technologies, this work might open a new territory for SiC-based quantum devices with many advanced properties of the host material.

Achieving a high photon count rate in digital time-correlated single photon counting using a hybrid photodetector.

We report an enhanced photon count rate in a digitally implemented time-correlated single-photon counting (TCSPC) system by utilizing a hybrid photodetector (HPD). In our digital TCSPC scheme, the photoelectronic responses from a single photon-sensitive photodetector are digitally analyzed through a high-speed analog-to-digital convertor (ADC). By virtue of the HPD which provides nearly a constant signal gain, the single-photon pulses can be effectively distinguished from pulses of simultaneously detected multiple photons by the pulse heights. Consequently, our digital TCSPC system can selectively collect single-photon signals even in the presence of intense multi-photon detections with its temporal accuracy not to be compromised. In our experiment of fluorescence lifetime measurement, the maximum count rate of single photons nearly reached the theoretical limit given by the Poisson statistics. This demonstrated that the digital TCSPC combined with the HPD provides an ultimate solution for the TCSPC implementation for high photon count rates.

Optimal Filtering of Overlapped Pulses in Microcalorimeter Data.

Here we present a general algorithm for processing microcalorimeter data with special applicability to data with high photon count rates. Conventional optimal filtering, which has become ubiquitous in microcalorimeter data processing, suffers from its inability to recover overlapped pulses without sacrificing spectral resolution. The technique presented here was developed to address this particular shortcoming, and does so without imposing any assumptions beyond those made by the conventional technique. We demonstrate the algorithm's performance with a data set that approximately satisfies these assumptions, and which is representative of a wide range of microcalorimeter applications. We also apply the technique to a highly non-linear data set, examining the impact on performance in the limit that these assumptions break down.

A Compact High-Speed Active Quenching and Recharging Circuit for SPAD Detectors

A compact high-speed active quenching and recharging circuit (AQRC) is proposed for single-photon avalanche diode (SPAD) detectors fabricated in standard 0.18 μm CMOS technology. A novel sensing and quenching scheme is employed to speed up the process of avalanche detection, enabling a low afterpulsing probability and a high photon-counting rate. The simulation and experimental results indicate that the sensing and quenching time is reduced down to 0.7 ns and the maximum photon-counting rate is close to 200 Mcps (counts per second), meanwhile the afterpulsing probability as low as 0.75% is obtained. Due to the compact configuration, the area occupation of the AQRC is only 306 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Such outstanding advantages suggest that the proposed AQRC is very suitable for the miniaturized and high-speed SPAD-array detectors.

High-rate X-ray spectroscopy in mammography with photon counting detectors using a limited number of energy bins

Direct measurement of mammographic X-ray spectra under clinical conditions can be useful for quality control (QC) in mammography for estimating image quality and patient dose. The measurement of mammographic X-ray spectra using the traditional detectors with multi-channel pulse height analyzer (MCA) systems is challenging because of the limitations imposed on measurements with high energy resolution at high photon counting rates, as well as geometrical restrictions, especially in a hospital environment. Semiconductor photon-counting detectors equipped with faster electronics enable utilization in somewhat high count rate situations at the expense of decreased energy resolution. This work presents a method for estimating mammography X-ray spectra from measurements acquired with a multi-energy bin photon counting detector. Simulation tests were conducted out for different incident X-ray spectra, energy thresholds and for multiple noise realizations assuming an ideal photon-counting X-ray detector with three energy thresholds. In addition, experimental measurements of mammography X-ray spectra were estimated by using a high-count rate Gallium Arsenide (GaAs) photon counting detector (with two or four energy thresholds) and a high resolution X-ray spectroscopy detector with Cadmium Telluride (CdTe) sensor for comparison. Differences between half-value layer values (HVL) obtained from the estimated spectra using the proposed method were found to be within 0.04 mm of the true values. This proposed method could be an attractive tool for laboratory research and calibration of photon-counting detectors.

High photon count rates improve the quality of super-resolution fluorescence fluctuation spectroscopy

Probing the diffusion of molecules has become a routine measurement across the life sciences, chemistry and physics. It provides valuable insights into reaction dynamics, oligomerisation, molecular (re-)organisation or cellular heterogeneities. Fluorescence correlation spectroscopy (FCS) is one of the widely applied techniques to determine diffusion dynamics in two and three dimensions. This technique relies on the temporal autocorrelation of intensity fluctuations but recording these fluctuations has thus far been limited by the detection electronics, which could not efficiently and accurately time-tag photons at high count rates. This has until now restricted the range of measurable dye concentrations, as well as the data quality of the FCS recordings, especially in combination with super-resolution stimulated emission depletion (STED) nanoscopy.Here, we investigate the applicability and reliability of (STED-)FCS at high photon count rates (average intensities of more than 1 MHz) using novel detection equipment, namely hybrid detectors and real-time gigahertz sampling of the photon streams implemented on a commercial microscope. By measuring the diffusion of fluorophores in solution and cytoplasm of live cells, as well as in model and cellular membranes, we show that accurate diffusion and concentration measurements are possible in these previously inaccessible high photon count regimes. Specifically, it offers much greater flexibility of experiments with biological samples with highly variable intensity, e.g. due to a wide range of expression levels of fluorescent proteins. In this context, we highlight the independence of diffusion properties of cytosolic GFP in a concentration range of approx. 0.01–1 µm. We further show that higher photon count rates also allow for much shorter acquisition times, and improved data quality. Finally, this approach also pronouncedly increases the robustness of challenging live cell STED-FCS measurements of nanoscale diffusion dynamics, which we testify by confirming a free diffusion pattern for a fluorescent lipid analogue on the apical membrane of adherent cells.

Active Feedback 3D Single-Molecule Tracking

Single molecule tracking has the potential to revolutionize the study of biological systems. However, most current single molecule imaging and tracking methods are limited to two dimensions. Meanwhile, real-time 3D single molecule tracking methods, which use active feedback to "lock-on" to single molecules in solution have until now been limited to observation times of 500 msec or less, greatly limiting their utility. Recently we developed a real-time 3D single particle tracking method known as 3D Dynamic Photon Localization Tracking (3D-DyPLoT). 3D-DyPLoT dynamically scans a focused laser spot in 3D with a tunable acoustic gradient lens and a 2D electro-optic deflector and has demonstrated real-time tracking at high diffusive speeds (up to 20 µm2/s) and low photon count rates 10 kHz. Here we demonstrate that the high tracking speed, sensitivity, and robustness of 3D-DyPLoT make it ideally suited active feedback 3D single molecule tracking. By implementing optimized tracking parameters based on single molecule model simulation, 3D-DyPLoT can continuously track single fluorescent dye molecules for several minutes at a time, two orders of magnitudes longer than previously reported methods. We demonstrate the application of this new single molecule tracking microscopy to track the free, 3D diffusion of DNA, RNA and proteins in solution. With two-color observation channels, 3D-DyPLoT was also applied to observing the transcription of single DNA molecules in solution by monitoring the real-time production of mRNA. This real-time 3D single molecule tracking method promises to be powerful tool for capturing the dynamics of single biomolecules at high speeds and over 3D distances. (Supported by NIH R35GM124868 and NSF 1847899).

The Heidelberg compact electron beam ion traps.

Electron beam ion traps (EBITs) are ideal tools for both production and study of highly charged ions (HCIs). In order to reduce their construction, maintenance, and operation costs, we have developed a novel, compact, room-temperature design, the Heidelberg Compact EBIT (HC-EBIT). Four already commissioned devices operate at the strongest fields (up to 0.86 T) reported for such EBITs using permanent magnets, run electron beam currents up to 80 mA, and energies up to 10 keV. They demonstrate HCI production, trapping, and extraction of pulsed Ar16+ bunches and continuous 100 pA ion beams of highly charged Xe up to charge state 29+, already with a 4 mA, 2 keV electron beam. Moreover, HC-EBITs offer large solid-angle ports and thus high photon count rates, e.g., in x-ray spectroscopy of dielectronic recombination in HCIs up to Fe24+, achieving an electron-energy resolving power of E/ΔE > 1500 at 5 keV. Besides traditional on-axis electron guns, we have also implemented a novel off-axis gun for laser, synchrotron, and free-electron laser applications, offering clear optical access along the trap axis. We report on its first operation at a synchrotron radiation facility demonstrating the resonant photoexcitation of highly charged oxygen.

Development of LSI for a new kind of photon-counting computed tomography using multipixel photon counters

X-ray imaging with computed tomography (CT) is widely used for nondestructive imaging of the interior of the human body. In the next decade, photon-counting X-ray CT is expected to reduce the dose needed and enable multicolor imaging. Recently, we proposed a novel photon-counting method that uses a multipixel photon counter (MPPC), with a significantly high signal gain (∼106) and fast temporal response (a few nanoseconds), combined with a high-speed scintillator. To realize photon-counting CT imaging in a wide area irradiated by an extremely high X-ray flux (106-107 Hz/mm2), a multichannel MPPC system is required. Thus, we developed a large-scale integrated circuit (LSI) with ultrafast signal-processing capability for use with a 16-channel MPPC. The developed LSI can extract a pulse current from an MPPC array with a large detector capacitance (∼200 pF) by utilizing an electrical circuit with low input impedance. The LSI offers a high photon count rate above 25 MHz/pixel with noise equal to 1.7 μA for a dynamic range of ∼ 1.3 mA and an energy resolution of 32 % (FWHM) at 60 keV, thereby enabling ultrafast multicolor CT imaging.

Tunable and high-purity room temperature single-photon emission from atomic defects in hexagonal boron nitride

Two-dimensional van der Waals materials have emerged as promising platforms for solid-state quantum information processing devices with unusual potential for heterogeneous assembly. Recently, bright and photostable single photon emitters were reported from atomic defects in layered hexagonal boron nitride (hBN), but controlling inhomogeneous spectral distribution and reducing multi-photon emission presented open challenges. Here, we demonstrate that strain control allows spectral tunability of hBN single photon emitters over 6 meV, and material processing sharply improves the single photon purity. We observe high single photon count rates exceeding 7 × 106 counts per second at saturation, after correcting for uncorrelated photon background. Furthermore, these emitters are stable to material transfer to other substrates. High-purity and photostable single photon emission at room temperature, together with spectral tunability and transferability, opens the door to scalable integration of high-quality quantum emitters in photonic quantum technologies.

Simulation results for PLATO: a prototype hybrid X-ray photon counting detector with a low energy threshold for fusion plasma diagnostics

PLATO is a prototype hybrid X-ray photon counting detector that has been designed to meet the specifications for plasma diagnostics for the WEST tokamak platform (Tungsten (W) Environment in Steady-state Tokamak) in southern France, with potential perspectives for ITER. PLATO represents a customized solution that fulfills high sensitivity, low dispersion and high photon counting rate. The PLATO prototype matrix is composed of 16 × 18 pixels with a 70 μm pixel pitch. New techniques have been used in analog sensitive blocks to minimize noise coupling through supply rails and substrate, and to suppress threshold dispersion across the matrix. The PLATO ASIC is designed in CMOS 0.13 μm technology and was submitted for a fabrication run in June 2016. The chip is designed to be bump-bonded to a silicon sensor. This paper presents pixel architecture as well as simulation results while highlighting novel solutions.

Application of an ePix100 detector for coherent scattering using a hard X-ray free-electron laser.

A prototype ePix100 detector was used in small-angle scattering geometry to capture speckle patterns from a static sample using the Linac Coherent Light Source (LCLS) hard X-ray free-electron laser at 8.34 keV. The average number of detected photons per pixel per pulse was varied over three orders of magnitude from about 23 down to 0.01 to test the detector performance. At high average photon count rates, the speckle contrast was evaluated by analyzing the probability distribution of the pixel counts at a constant scattering vector for single frames. For very low average photon counts of less than 0.2 per pixel, the `droplet algorithm' was first applied to the patterns for correcting the effect of charge sharing, and then the pixel count statistics of multiple frames were analyzed collectively to extract the speckle contrast. Results obtained using both methods agree within the uncertainty intervals, providing strong experimental evidence for the validity of the statistical analysis. More importantly it confirms the suitability of the ePix100 detector for X-ray coherent scattering experiments, especially at very low count rates with performances surpassing those of previously available LCLS detectors.

Efficient single photon source based on μ-fibre-coupled tunable microcavity.

Efficient and fast on-demand single photon sources have been sought after as critical components of quantum information science. We report an efficient and tunable single photon source based on an InAs quantum dot (QD) embedded in a photonic crystal cavity coupled with a highly curved μ-fibre. Exploiting evanescent coupling between the μ-fibre and the cavity, a high collection efficiency of 23% and Purcell-enhanced spontaneous emissions are observed. In our scheme, the spectral position of a resonance can be tuned by as much as 1.5 nm by adjusting the contact position of the μ-fibre, which increases the spectral coupling probability between the QD and the cavity mode. Taking advantage of the high photon count rate and the tunability, the collection efficiencies and the decay rates are systematically investigated as a function of the QD–cavity detuning.

Probing solid-state nanopores with light for the detection of unlabeled analytes.

Nanopore sensing has enabled label-free single-molecule measurements on a wide variety of analytes, including DNA, RNA, and protein complexes. Much progress has been made toward biotechnological applications; however, electrically probing the ion current introduces nonideal noise components. Here we further develop a method to couple an ionic current to a photon-by-photon counting of fluorescent signal from Ca2+-sensitive dyes and demonstrate label-free optical detection of biopolymer translocation through solid-state nanopores using TIRF and confocal microscopy. We show that by fine adjustment of the CaCl2 gradient, EGTA concentration, and voltage, the optical signals can be localized to the immediate vicinity of the pore. Consequently, the noise spectral density distribution in the optical signal exhibits a nearly flat distribution throughout the entire frequency range. With the use of high-speed photon counting devices in confocal microscopy and higher photon count rates using stronger light sources, we can improve the signal-to-noise ratio of signal acquisition, while the use of wide-field imaging in TIRF can allow for simultaneous quantitative imaging of large arrays of nanopores.