Scintillation readout with MAPD array for gamma spectrometer

Novel micropixel avalanche photodiodes (MAPD) with super high pixel density

Effects of high pixel density on reading comprehension, proofreading performance, mood state, and physical discomfort

In the past decades significant improvement of the performance of III-V Geiger-mode APDs (GmAPD) has been achieved in Near Infrared (NIR) and Short Wavelength Infrared (SWIR) wavelengths. In order to meet the challenge to GmAPDs in visible wavelength for some special military and space applications, Acqubit developed a GaAs-based InGaP APD with a substrate removal structure. With a proprietary mesa passivation process, very low dark current, ~0.5 nA in a 50 um diameter device or 25 uA/cm2, was demonstrated just before breakdown at room temperature. Sufficient device thickness ensured an external quantum efficiency (QE) about 50% at 532 nm without a bottom reflector. The combination of mesa structure and substrate removal process greatly suppressed the array pixel crosstalk and afterpulsing while maintaining a high QE and photon detection efficiency (PDE). In this paper we will report the progress of the GmAPD detectors and arrays with low DCR and high PDE at 532 µm.

This paper presented a new detector module consisting of a micropixel avalanche photodiode (MAPD-3NM), LaBr3:Ce scintillator, and a compact read-out interface system for detecting gamma-rays in a wide energy range. The MAPD array (4 × 4 channels) was assembled using a single MAPD-3NM characterized by its high photon detection efficiency (∼25%), pixel density (10 000 pixels/mm2), low operation voltage (74.5 V), and low dark current. An active area of a single MAPD-3NM was 3.7 × 3.7 mm2, while this value was 17 × 17 mm2 for the assembled array with pixel density of 2190 000. The size of the tested LaBr3:Ce scintillator was 15 × 15 × 15 mm3. According to the characteristics of the detector module, a compact read-out interface device (SPECTRIG MAPD) was developed. SPECTRIG MAPD was designed as a miniature device with low power consumption, which continues to provide a wide spectrum of functions needed for measurement and test silicon photomultipliers (SiPM) and scintillation detectors on their basis. The various experiments were implemented to test the detection performance of a detector module to gamma radiation in the range from 30 keV to 4400 keV.

With high specificity for malignant breast lesions, dedicated-breast molecular imaging systems such as positron emission mammography (PEM) have potential to improve the sensitivity of cancer in women with radio-dense breasts and to reduce the false-positive rate of breast screening when used as a diagnostic adjunct. For high signal-to-noise ratio and to minimize the patient dose, scintillation detectors in a PEM system must have high annihilation photon detection efficiency. This efficiency can be increased by accepting annihilation photons from wider incident angles and by using depth-of-interaction (DOI) measurement within a scintillation crystal to minimize parallax blurring. We have developed a dual-ended readout block (DERB) detector that uses asymmetry of signals from photodetectors on either end of a scintillation array to measure DOI and uses Anger Logic with light sharing to identify interacting crystal elements while minimizing the number of photodetectors required. A prototype DERB detector was constructed from two arrays of silicon photomultipliers (SiPM), two glass optical diffusers, and an array of LYSO scintillation crystals. Assembled, each of the 2 × 2 SiPM arrays detect photons that are dispersed via the optical light diffusers originating from either end of 3 × 3 scintillation crystal elements. We evaluated the ability of the detector to identify the crystal index, resolve DOI, and discriminate energy. The DERB detector was able to clearly identify interacting crystal elements, to measure DOI with ̃5mm resolution in 2mm × 2mm × 20mm crystals, and to achieve an average energy resolution of ̃20%. The DERB detector characteristics suggest that it can be used to reduce the parallax effect in PEM systems without increasing the number of required photodetectors. Further investigation is warranted to improve performance with high optical photon detection efficiency photodetectors.

The Multi-Pixel Photon Counter (MPPC) is a Geiger-mode avalanche photo-diode (APD) developed by Hamamatsu Corp. We propose that it could be a suitable photo-sensor for next-generation time-of-flight PET detectors due to its high photon detection efficiency. We concentrate on the measurement of coincidence timing performance of various MPPCs in conjunction with LYSO crystal scintillators. With 3 mm times 3 mm devices of 50 mum sub-pixels coupled to 3 mm times 3 mm times 10 mm LYSO crystals, we have demonstrated a strong dependence of timing performance on over-voltage and temperature, and analyzed how changes in photon detection efficiency and dark counts would explain the measurements. The best coincidence timing resolution we have achieved between two identical LYSO/MPPC detectors was 240 ps in FWHM. This was worse than the timing resolution of 220 ps obtained with a Hamamatsu H6533 fast PMT, and contradicted the expected improvement from higher photon detection efficiency. The contradiction could be explained by the slow rise-time of MPPC pulse shape, transit time spread, dark counts and electronic noise from the large capacitance of the MPPC. In particular, the slow rise-time of the MPPC pulse suggests the need for a very low trigger threshold on the timing circuit. Since this makes the detector system more sensitive to noise, this poses additional challenges for ganging multiple devices together into a commercially viable time-of-flight PET block detector. We will discuss this work in detail including other challenge imposed by MPPC characteristics.

Silicon photomultipliers (SiPMs) are arrays of many single-photon avalanche diodes (SPADs), all connected in parallel. Each SPAD is sensitive to single photons and the SiPM gives an output proportional to the number of detected photons. These sensors are becoming more and more popular in different applications, from high-energy physics to spectroscopy, and they have been significantly improved over last years, decreasing the noise, increasing the cell fill-factor (FF) and thus achieving very high photon-detection efficiency (PDE). In FBK (Trento, Italy), we developed new SiPM technologies with high-density (HD) and, more recently, ultra-high-density (UHD) of cells (i.e. density of SPADs). These technologies employ deep-trenches between cells, for electrical and optical isolation. As an extreme case the smallest-cell, SiPM, i.e. with 5μm cell pitch, has about 40000 SPADs per squared millimeter. Such small SPAD dimensions gives a significantly high dynamic range to the SiPM. These small-cells SiPM have a lower correlated noise (including lower afterpulsing probability) and a faster recharge time (in the order of few nanoseconds), and they also preserve a very good detection efficiency (despite the small SPAD dimension).

Single-photon detector (SPD) as an essential building block for detecting and counting photons, plays a fundamental role in quantum technologies. In this work, we propose an efficient workflow of modeling SPDs based on emerging one-dimensional materials, i.e. nanowires, utilizing avalanche breakdown in reverse biased condition. Comparing to another extensively studied platform, superconducting nanowire SPDs, avalanche nanowire device is demonstrated in this work to promise comparable performance (e.g. high photon detection efficiency (PDE) and and low dark count rate (DCR)) but without working at extreme cryogenic temperature (4K). The proposed workflow explored to maximize computational workload and balancing between time-consuming drift-diffusion simulation and fast script-based post-processing, and in timely convergence we were able to predict a suite of key performance metrics for single-photon SPDs, including breakdown voltage, PDE, DCR, and time resolution.

Abstract. The Synthetic Aperture Radar (SAR) satellite Sentinel-1 provides excellent traffic infrastructure monitoring capabilities due to its short revisit time, wide-scale coverage and free of charge data policy. However, pixels from Sentinel-1 have a medium spatial resolution so that traffic infrastructure is only covered by a few pixels. Moreover, Interferometric Synthetic Aperture Radar (InSAR) yields deformation time series for coherent pixels only, thus limiting the number of pixels reporting the ground motion at traffic infrastructure. Although various InSAR time series methods have been successfully applied for traffic infrastructure monitoring, the selection of appropriate methods achieving a high pixel density has not yet been evaluated. In this study, we test whether we can improve the monitoring capabilities by combining different InSAR time series methods. On the one hand, we applied widely used Stanford Method for Persistent Scatterers (StaMPS) as a baseline method to retrieve the deformation time series. On the other hand, we enhanced the phase quality in a pre-processing step using the Phase-Linking (PL) approach and afterwards estimated the deformation time series also with StaMPS based on pixels selected by PL. We compared and evaluated the achieved pixel densities from both methods at main roads, highways and railways in a study area in Germany. We found that the InSAR time series methods selected complementary sets of pixels at all traffic infrastructure types. Moreover, the results indicate a great potential for railway monitoring using Sentinel-1 InSAR due to both high pixel density and homogeneous spatial distribution of pixels. Interestingly, coherent scatterers selected by StaMPS were observed to coincide with large traffic signs at highways which show a double-bounce scattering in the amplitude images. This study shows the benefits of combining PL and StaMPS for increased pixel density at traffic infrastructure and confirms Sentinel-1 data as a suitable data source for traffic infrastructure monitoring.

Studies on a silicon-photomultiplier-based camera for Imaging Atmospheric Cherenkov Telescopes

ABSTRACTPolycrystalline silicon (p-Si) TFT offers higher aperture ratio with integrated driver circuits compared to the conventional a-Si TFT in AM-LCD application. The advantages of the p-Si TFT as the pixel switching element will be more pronounced for AM-LCDs with large number of scan lines and/or high pixel density. This paper reviews challenges and issues associated with the technology of p-Si TFT, particularly in active silicon layer deposition, solid phase and laser crystallization, hydrogenation, leakage current, performance of different device architectures and reliability. Critical issues affecting the p-Si TFT AMLCD pixel design are analyzed, including: lithographic resolution and overlay accuracy, pixel density and aspect ratio, display format, storage to LC capacitance ratio, and gate dielectric thickness. Predictions on the regimes of dominance for different flat-panel technologies by advantages in performance and-or cost with respect to panel size and pixel density will be presented.

The design of a photodetector unit of a new Shashlyk EM calorimeter for COMPASS II

This work presents the development and experimental characterization of a compact ultraviolet (UV) telescope based on silicon photomultipliers (SiPMs) designed for the detection of faint atmospheric optical tracks. Such transient optical phenomena include meteors, transient luminous events (TLEs), space debris reentries, and other faint atmospheric emissions. Nuclearite-induced atmospheric emission is considered as a benchmark case for evaluating the expected signal levels of rare luminous track events. We detail the fabrication, assembly, and testing of the SiPM sensor array, comprising parallel Geiger-mode avalanche diodes with high fill factor and photon detection efficiency, alongside custom readout electronics using self-triggering ASICs, precision optical components, and a stable mechanical mount. This photon-counting telescope provides a compact and mechanically robust alternative to conventional PMT-based systems, with demonstrated capability for detecting low-light atmospheric tracks under controlled laboratory conditions.

Identification of the number of graphene layers using an optical microscope images taken at various magnifications is investigated from the viewpoint of simple wide-area inspection. For graphene on 300-nm-thick SiO2, combination of red and green color contrast gives more accurate contrast value and provides better contrast even at the low magnification as compared with the single color channel contrast. The color combination with suitable weighting factors taking account of light wavelength and intensity dependences of the system response results in the contrast that agrees well with the theoretical values from Fresnel's law. Simple image processing is also investigated to improve the signal-to-noise ratio (SNR) of the image. Median filtering improves the SNR of the image having high pixel density, whereas dithering is effective for the low magnification image having block noise due to low pixel density.

High pixel density, efficient color splitting, a compact structure, superior quantum efficiency, and low power consumption are all important features for contemporary color-image sensors. In this study, we developed a surface plasmonics-based color-image sensor displaying a high photoelectric response, a microlens-free structure, and a zero-bias working voltage. Our compact sensor comprised only (i) a multifunctional electrode based on a single-layer structured aluminum (Al) film and (ii) an underlying silicon (Si) substrate. This approach significantly simplifies the device structure and fabrication processes; for example, the red, green, and blue color pixels can be prepared simultaneously in a single lithography step. Moreover, such Schottky-based plasmonic electrodes perform multiple functions, including color splitting, optical-to-electrical signal conversion, and photogenerated carrier collection for color-image detection. Our multifunctional, electrode-based device could also avoid the interference phenomenon that degrades the color-splitting spectra found in conventional color-image sensors. Furthermore, the device took advantage of the near-field surface plasmonic effect around the Al-Si junction to enhance the optical absorption of Si, resulting in a significant photoelectric current output even under low-light surroundings and zero bias voltage. These plasmonic Schottky-based color-image devices could convert a photocurrent directly into a photovoltage and provided sufficient voltage output for color-image detection even under a light intensity of only several femtowatts per square micrometer. Unlike conventional color image devices, using voltage as the output signal decreases the area of the periphery read-out circuit because it does not require a current-to-voltage conversion capacitor or its related circuit. Therefore, this strategy has great potential for direct integration with complementary metal-oxide-semiconductor (CMOS)-compatible circuit design, increasing the pixel density of imaging sensors developed using mature Si-based technology.