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PROBA-3 is an ESA mission aimed at the demonstration of formation flying performance of two satellites that will form a giant coronagraph in space. The first spacecraft will host a telescope imaging the solar corona in visible light, while the second, the external occulter, will produce an artificial eclipse. This instrument is named ASPIICS (Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun). To accomplish the payload's scientific tasks, PROBA-3 will ensure sub-millimeter reciprocal positioning of its two satellites using closed-loop on-board metrology. Several metrology systems will be used and the Shadow Position Sensors (SPS) subsystem senses the penumbra around the instrument aperture and returns the 3-D displacement of the coronagraph satellite, with respect to its nominal position, by running a dedicated algorithm. In this paper, we describe how the SPS works and the choices made to accomplish the mission objectives.

PROBA-3 is a space mission of the European Space Agency that will test, and validate metrology and control systems for autonomous formation flying of two independent satellites. PROBA-3 will operate in a High Elliptic Orbit and when approaching the apogee at 6·104 Km, the two spacecraft will align to realize a giant externally occulted coronagraph named ASPIICS, with the telescope on one satellite and the external occulter on the other one, at inter-satellite distance of 144.3 m. The formation will be maintained over 6 hrs across the apogee transit and during this time different validation operations will be performed to confirm the effectiveness of the formation flying metrology concept, the metrology control systems and algorithms, and the spacecraft manoeuvring. The observation of the Sun's Corona in the field of view [1.08;3.0]RSun will represent the scientific tool to confirm the formation flying alignment. In this paper, we review the mission concept and we describe the Shadow Position Sensors (SPS), one of the metrological systems designed to provide high accuracy (sub-millimetre level) absolute and relative alignment measurement of the formation flying. The metrology algorithm developed to convert the SPS measurements in lateral and longitudinal movement estimation is also described and the measurement budget summarized.

PROBA3 is the first high precision formation flying (FF) mission under responsibility of the European Space Agency (ESA). It is a technology mission devoted to in-orbit demonstration of the FF techniques, with two satellites kept at an average inter-satellite distance of 144m. The guiding scientific rationale is to realize a diluted coronagraph with the telescope (ASPIICS) on one satellite and the external occulter on the other satellite to observe the inner Solar corona at high spatial and temporal resolution, down to 1.08R⊙. The two spacecraft will be orbiting in a high eccentricity geocentric trajectory with perigee at 600km and the apogee at 60000Km and with an orbital period of 19hrs. The FF acquisition and operations will last about 6 hrs around the apogee and different metrology systems will be used for realizing and controlling the FF. The alignment active most critical sub-system is the Shadow Positioning Sensors (SPS), a series of Si-PM (Silicon Photomultiplier) disposed around the ASPIICS telescope's entrance aperture and measuring the proper positioning of the penumbra generated by the occulter at the center of the coronagraph’s optical reference frame. The FF alignment measurement accuracies required to the SPS are: 500μm for lateral movements and 50mm for longitudinal movements. This paper gives an overview of the opto-mechanical and electronic design and of the software algorithm for the FF intersatellite positioning. The expected performance of the SPS metrology system are reported.

This work addresses a systematic and in-depth electro-optical characterization of the Multi-Pixel Photon Counter (MPPC) sensors constituting the camera detection system at the focal plane of the ASTRI telescope prototype. The paper reports the experimental results of a large set of measurements on the MPPC devices in order to provide a reliable qualification of the detector performance and evaluate its compliance with the telescope focal plane requirements. In particular, breakdown voltage, internal gain, dark count rate, cross-talk and extra-charge probability, and absolute photon detection efficiency measurements are performed on the basic sensor device unit as a function of the detector operating conditions.

A comprehensive and in-depth characterization procedure for obtaining very accurate measurements on silicon photomultiplier detectors (SiPMs) is here described. A large amount of optical tests are systematically carried out and discussed in terms of the most important SiPM performance parameters; in particular, an accurate estimation of the photon detection efficiency in the 350-900-nm wavelength spectral range and in steps of 10 nm is achieved, based on the single-photon counting technique, with substraction of the dark noise contribution and avoiding the additional noise sources of crosstalk and afterpulsing. Some recently produced detectors are analyzed and their relevant electro-optical parameters are evaluated in order to demonstrate the effectiveness and efficacy of the adopted characterization procedure and data-handling protocols in assessing the overall SiPM performance, regardless of the specific device tested. Tests repeatibility is carefully verified and all the evaluated parameter trends are proved to be compatible with the physics theory of the SiPM device.

The present work aims to address a comprehensive analytical analysis of a new accurate equivalent electrical model of silicon photomultiplier (SiPM) detectors. The proposed circuit model allows to truthfully reproduce the output signal waveform generated by the light sensors apart from the specific technology adopted for the fabrication process, and can also be profitably exploited to perform reliable circuit-level simulations. A detailed and in-depth investigation of the functional parameters involved in the output pulse signals is here developed, and the most significant physical relationships are analytically derived as well. Experimental measurements are finally carried out on real devices, in order to validate the accuracy of the attained expressions, and good fittings are achieved between the analytical curve plots and the associated measurements results. The adopted analysis turns out to be particularly helpful when designing an optimum front-end architecture for SiPM detectors, since the performance of the entire detection system, especially in terms of dynamic range and timing resolution, can be accurately predicted as a function of the SiPM model parameters and the foremost features of the coupled front-end electronics.

The present work introduces an improved SPICE equivalent electrical model of silicon photomultiplier (SiPM) detectors, in order to simulate and predict their transient response to avalanche triggering events. In particular, the developed circuit model provides a careful investigation of the magnitude and timing of the read-out signals and can therefore be exploited to perform reliable circuit-level simulations. The adopted modeling approach is strictly related to the physics of each basic microcell constituting the SiPM device, and allows the avalanche timing as well as the photodiode current and voltage to be accurately simulated. Predictive capabilities of the proposed model are demonstrated by means of experimental measurements on a real SiPM detector. Simulated and measured pulses are found to be in good agreement with the expected results.

International audience; Context: A new extremely high speed photon-counting photometer, Iqueye, has been installed and tested at the New Technology Telescope, in La Silla. Aims: This instrument is the second prototype of a ``quantum'' photometer being developed for future Extremely Large Telescopes of 30-50 m aperture. Methods: Iqueye divides the telescope aperture into four portions, each feeding a single photon avalanche diode. The counts from the four channels are collected by a time-to-digital converter board, where each photon is appropriately time-tagged. Owing to a rubidium oscillator and a GPS receiver, an absolute rms timing accuracy better than 0.5 ns during one-hour observations is achieved. The system can sustain a count rate of up to 8 MHz uninterruptedly for an entire night of observation. Results: During five nights of observations, the system performed smoothly, and the observations of optical pulsar calibration targets provided excellent results.

We present the preliminary results of the characterization of silicon detectors in terms of Photon Detection Efficiency (PDE). The precision measurements are performed at controlled temperature, using a specially suited setup based on a monochromator, an integrating sphere to randomize the incident light and a calibrated reference photodiode. We exploit a measurement technique that we recently devised, based on single photon counting with subtraction of dark noise, and avoiding as much as possible cross-talk and afterpulses. We describe in detail the experimental setups and the techniques utilized to measure the PDE. The achieved results are here discussed in order to establish a methodology capable to give very precise PDE values for solid-state photomultiplier detectors.

In this paper we present the results of the first electrical and optical characterization performed on 1 mm2 total area Silicon Photomultipliers (SiPM) fabricated in standard silicon planar technology at the STMicroelectronics Catania R&D clean room facility. The device consists of 289 microcells and has a geometrical fill factor of 48%. Breakdown voltage, gain, dark noise rate, crosstalk, photon detection efficiency and linearity have been measured in our laboratories. The optical characterization has been performed by varying the temperature applied to the device. The results shown in the manuscript demonstrate that the device already exhibits relevant features in terms of low dark noise rate and inter-pixel crosstalk probability, high photon detection efficiency, good linearity and single photoelectron resolution. These characteristics can be considered really promising in view of the final application of the photodetector in the Positron Emission Tomography (PET).

In the framework of a national collaboration to bring Quantum Optics concepts to Astronomy, we are involved in finding suitable detectors for this novel application. At ‘INAF Osservatorio Astrofisico di Catania’ and ‘INFN – Laboratori Nazionali del Sud’ laboratories, measurements of electro-optical parameters, such as photon detection efficiency (PDE), linearity, dark counts and after pulsing probability, as well as of timing resolution, have been carried out. These measurements have been done on silicon detectors, such as single photon avalanche diode (SPAD) (both single element and array), and silicon photon multiplier (SiPM), operating in the photon counting regime.

This paper describes the results obtained so far with AquEYE, a single photon counting, fixed aperture photometer for the Asiago 182 cm telescope. AquEYE has been conceived as a prototype of a truly 'quantum' photometer for future Extremely Large Telescopes of 30-50 m aperture. This prototype is characterized by four independent channels equipped with single photon avalanche diodes (SPADs) as detectors. The counts from the four channels are acquired by a TDC board which has a nominal 25 ps time tagging capability. Taking into account the 35 ps jitter in the SPAD itself, the overall precision of the time tags is of the order of 50 ps. The internal oscillator is locked to an external rubidium clock; a GPS pulse per second is collected by the TDC itself to obtain a UTC reference. The maximum photon count rate which the present system can sustain is 12 MHz.

The fabrication of silicon shallow junction photodiodes is a relevant topic for the detection of blue and near ultraviolet weak photon fluxes. In this paper we present a simple model to calculate the quantum detection efficiency (QDE) of a Geiger mode avalanche photodiode (GMAP) as a function of the dead layer thickness above the junction depletion layer. A comparison between calculated and experimental data is also presented. Moreover, by using the same model, an analysis of the QDE at 420 nm wavelength of conventional GMAPs based on shallow N+-P and P+-N junctions is given.

In this paper, we present the results of the first noise characterization performed on our novel 100-channel silicon photomultiplier. We have improved our previous single-photon avalanche photodiode technology in order to set up a working device with outstanding features in terms of single-photon resolving power up to R = 45, timing resolution down to 100 ps, and photon-detection efficiency of 14% at 420 nm. Tests were performed, and features were measured, as a function of the bias voltage and of the incident photon flux. A dedicated data-analysis procedure was developed that allows one to extract at once the relevant parameters and quantify the noise.

In this paper, we present the results of the charge and time characterization performed on our novel 100-channel silicon photomultiplier. We have improved our previous single-photon-avalanche-diode technology in order to set up a working device with outstanding features in terms of single-photon resolving power up to R = 45, a timing resolution down to 100 ps, and photon-detection efficiency of 14% at 420 nm. Tests were performed, and features were measured as a function of the bias voltage and of the incident photon flux. A dedicated data analysis procedure was developed that allows to extract at once the relevant parameters from the amplitude spectra and to determine the timing features.

In this paper we present the results of the first electrical and optical characterization performed on STMicroelectronics new photosensor technology based on silicon single-photon avalanche photodiodes (SPAD). On the prospective of the design and the manufacturing of large-area silicon photomultipliers to be used as photodetectors for nuclear medicine imaging applications, we have modified our previous SPAD technology by means of the integration of a high-value quenching resistor to the photodiode. Moreover, an appropriate antireflective coating layer and the reduction of the quasi-neutral region thickness above the thin junction depletion layer have been introduced in the process flow of the device to enhance its spectral response in blue and near ultraviolet wavelength ranges. High gain, low leakage currents, low dark noise, very good quantum detection efficiency in blue–near UV ranges and a good linearity of the photodiode response to the incident luminous flux are the main characterization results.

The fabrication of high sensitive diodes array is very attractive for spectroscopic and astronomical UV imaging applications, particularly when visible light rejection is required. Wide band gap materials are excellent candidates for UV “visible blind” detection. In this paper, we demonstrate an array of Schottky UV-diodes on 4H-SiC with a single pixel area of about 1.44 mm2 and a total area of about 29 mm2. The Schottky photodiodes are based on the pinch-off surface effect, the front electrode being an interdigit Ni2Si contact that allows the direct light exposure of the optically active device area. For the proposed array, the optically active area is about the 48 % of total area. The single pixel dark current was below 0.1 nA up to –50 V and a fabrication yield of about 90 % was observed. The external quantum efficiency of the proposed array exhibits a peak of 45 % at the 289 nm wavelength and a visible rejection ratio > 4 ×103.

In this paper, we present the results regarding the electrical and optical characterization of bidimensional arrays of silicon single photon avalanche photodiodes (SPAD). Low average dark count rates and crosstalk probability, good timing jitter and high quantum detection efficiency in the visible range have been measured over 5 × 5 SPAD arrays with 40 μm single pixel active area diameter. Moreover, a very good uniformity of these parameters has been found over the single pixels. These good electro-optical performances make our photodiodes attractive for the fabrication of arrays with a larger number of SPAD. In view of the design of a dense array to be used as a silicon photomultiplier (SiPM) for medical diagnostic tools, 5 × 5 SPAD arrays have been also tested in the photon-resolving mode. Charge spectra show that the arrays, in this configuration, allow to resolve several photoelectron peaks with a good single photoelectron resolution.

In this letter we present the results regarding the electrical and optical characterization of Geiger mode silicon avalanche photodiodes (GMAP) fabricated by silicon standard planar technology. Low dark count rates, negligible afterpulsing effects, good timing resolution and high quantum detection efficiency in all the visible range have been measured. The very good electro-optical performances of our photodiodes make them attractive for the fabrication of arrays with a large number of GMAP to be used both in the commercial and the scientific fields, as telecommunications and nuclear medical imaging.

In this paper a comprehensive analytical analysis is performed based on a new accurate electrical model of silicon photomultiplier (SiPM) detectors. The proposed circuit model allows to accurately reproduce the SiPM output time response regardless of the particular technology adopted for the fabrication process, and can also be profitably exploited to perform reliable circuit-level simulations. A novel expression of the detector photoelectron response due to a single photon absorption is systematically developed. The obtained waveform accurately reproduces the fast detector ignition, the ensuing avalanche self-quenching and the final slow recharging operation. Predictive capabilities of the adopted analytical model are demonstrated by means of experimental measurements on a real SiPM device.

The Cherenkov Telescope Array (CTA) is a worldwide new gene ration project aimed at realizing an array of a hundred ground based gamma-ray telescopes. ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana) is the Italian project whose primary target is the development of an end-to-end prototype, named ASTRI SST-2M, of the CTA small size class of telescopes devoted to investigation of the highest energy region, from 1 to 100 TeV. Next target is the implementation of an ASTRI/CTA mini-array based on seve n identical telescopes. Silicon Photo-Multipliers (SiPMs) are the semiconductor photosensor devices designated to constitute the camera detection system at the focal plane of the ASTRI telescopes. SiPM photosensors are suitable for the detection of the Cherenkov flashes, since they are very fast and sensitive to the light in the 300-700nm wavelength spectrum. Their drawbacks compared to the traditional photo-multiplier tubes are high dark count rates, after-pulsing and optical cross-talk contributions, and intrinsic gains strongly dependent on temperature. Nonetheless, for a single pixel, the dark count rate is well below the Night Sky Background, the effects of cross-talk and afterpulses are typically lower th an 20%, and the gain can be kept stable against temperature variations by means of adequate bias voltage compensation strategies. This work presents and discusses some experimental results from a large set of measurements performed on the SiPM sensors to be used for the ASTRI SST-2M prototype camera and on recently developed detectors demonstrating outstanding performance for the future evolution of the project in the ASTRI/CTA mini-array. Keywords: ASTRI, CTA, detectors, characterizations, phot on detection efficiency, silicon photomultipliers.

The Muon Portal Project goal is the design and construction of a working detector prototype in scale 1∶1, to inspect the content of travelling containers by means of the secondary cosmic-ray muon radiation and recognize high-Z hidden materials (U, Pu or other fissile samples). The radiographic image is obtained by reconstructing the input and output trajectories of each muon and consequently the scattering angle, exploiting two trackers placed above and below the container. The scan is performed without adding any external radiation, in a reasonable time (a few minutes) and with a good spatial and angular resolution. The detector consists of 8 planes segmented in 6 identical modules. Each module is made of scintillating strips with two WaveLength Shifting fibers (WLS) inside, coupled to Silicon photomultipliers. The customized read-out electronics employs trading programmable boards. Thanks to a smart read-out system, the number of output channels is reduced by a factor 10. The signals from the front-end modules are sent to the read-out boards, in order to convert the analog signal to a digital signal, by a comparison to a threshold. The data are pre-analyzed and stored into a data acquisition PC. Actually, an intense measurement and simulation campaign is in progress to characterize carefully the detector components. The first detection modules (1 × 3 m2) is now under construction. The detector architecture with a particular attention to the used electronics and the main preliminary results will be presented.

The Muon Portal Project aims at the construction of a large volume detector to inspect the content of travelling containers for the identification of high-Z hidden materials (U, Pu or other fissile samples), exploiting the secondary cosmic-ray muon radiation. An image of these materials is achieved reconstructing the deviations of the muons from their original trajectories inside the detector volume, by means of two particle trackers, placed one below and one above the container. The scan is performed without adding any external radiation, in a few minutes and with a high spatial and angular resolution. The detector consists of 4800 scintillating strips with two wavelength shifting (WLS) fibers inside each strip, coupled to Silicon photomultipliers (SiPMs). A smart strategy for the read out system allows a considerable reduction of the number of the read-out channels. Actually, an intense measurement campaign is in progress to carefully characterize any single component of the detector. A prototype of one of the 48 detection modules (1 × 3 m2) is actually under construction. This paper presents the detector architecture and the preliminary results.

The present paper is intended to implement and simulate the Extended Analogue Silicon-photomultiplier Integrated Read-Out Chip (EASIROC) fully analogue front-end model, in order to investigate its foremost characteristics and demonstrate its practical effectiveness when its analogue inputs are driven by the silicon photomultiplier (SiPM) signals. The circuit models of all functional blocks are described. Frequency and dynamic features of all circuit front-end sections are briefly addressed, and design mathematical equations are derived as well. PSPICE simulations of each single model are carried out to analyse and confirm its analogue behaviour.

This paper addresses a comprehensive analytical analysis of a new accurate electrical model of silicon photomultiplier (SiPM) detectors. The adopted circuit model allows to truly reproduce the SiPM output signal waveform apart from the specific technology employed for the fabrication process, and can also be profitably exploited to perform reliable circuit-level simulations. A novel analytical expression of the transient single-photoelectron response due to photon absorption is systematically developed. The attained function accurately reproduces the fast detector ignition, ensuing avalanche self-quenching, and final slow recharging operation. Predictive capabilities of the adopted analytical model are demonstrated by means of experimental measurements on a real detector.

Traditional techniques, such as those based on X-rays absorption, to inspect shipping container in search of potential fissile threats cannot be employed on occupied vehicles and are of limited use in presence of a large amount of shielding materials. To overcome such limitations, prototypes of detection systems employing the muon tomography technique, based on cosmic muon scattering from high-Z materials, are being tested worldwide. The Muon Portal project aims to build a large area muon detector (18 m2) for the inspection of TEU containers with good spatial and angular resolution. The detector is made by four XY tracking planes of plastic scintillator bars with embedded WLS fibers and SiPM readout, placed above and below the volume to be inspected. Different imaging and visualization algorithms are being designed and tested over tomographic scenarios simulated with a detailed software replica of the entire detector. Experimental tests of the individual detection modules are already in progress. The design and operational parameters of the portal under construction are reported, together with the preliminary detector tests and imaging results.

The Extended Analogue Silicon Photo-multiplier Integrated Read Out Chip, EASIROC, is a chip proposed as front-end of the camera at the focal plane of the imaging Cherenkov ASTRI SST-2M telescope prototype. This paper presents the results of the measurements performed to characterize EASIROC in order to evaluate its compliance with the ASTRI SST-2M focal plane requirements. In particular, we investigated the trigger time walk and the jitter effects as a function of the pulse amplitude. The EASIROC output signal is found to vary linearly as a function of the input pulse amplitude with very low level of electronic noise and cross-talk (, 21 pages, 14 figures

ASTRI is an Flagship Project led by the Italian National Institute of Astrophysics, INAF, strictly linked to the development of the ambitious Cherenkov Telescope Array, CTA. Primary goal of the ASTRI project is the design, production, installation and calibration of an end-to-end Small Size Telescope prototype, devoted to the investigation of the highest gamma-ray energy band, from a fraction of TeV up to 100 TeV and beyond. The telescope, named ASTRI SST-2M, is mainly characterized by an optical system in dual-mirror configuration and by a modular camera at the curved focal surface composed of a matrix of Silicon Photo-Multipliers photo-sensors. In this paper we present an overview of the mechanical, thermal and electrical concept design of the camera and of the related technological solutions adopted for the ASTRI SST-2M prototype.

The Cherenkov Telescope Array (CTA) is a new observatory for very high-energy (VHE) gamma rays. CTA has ambitions science goals, for which it is necessary to achieve full-sky coverage, to improve the sensitivity by about an order of magnitude, to span about four decades of energy, from a few tens of GeV to above 100 TeV with enhanced angular and energy resolutions over existing VHE gamma-ray observatories. An international collaboration has formed with more than 1000 members from 27 countries in Europe, Asia, Africa and North and South America. In 2010 the CTA Consortium completed a Design Study and started a three-year Preparatory Phase which leads to production readiness of CTA in 2014. In this paper we introduce the science goals and the concept of CTA, and provide an overview of the project., La lista completa de autores puede consultarse en el documento o en la página web de la revista., Facultad de Ingeniería

ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana), is a flagship project of the Italian Ministry of Education, University and Research whose main goal is the design and construction of an end-to-end prototype of the Small Size of Telescopes of the Cherenkov Telescope Array. The prototype, named ASTRI SST-2M, will adopt a wide field dual mirror optical system in a Schwarzschild-Couder configuration to explore the VHE range of the electromagnetic spectrum. The camera at the focal plane is based on Silicon Photo-Multipliers detectors which is an innovative solution for the detection astronomical Cherenkov light. This contribution reports some preliminary results on the evaluation of the optical cross talk level among the SiPM pixels foreseen for the ASTRI SST-2M camera., Comment: 7 pages, 4 figures

The Muon Portal is a recent Project [1] which aims at the construction of a 18 m2 tracking detector for cosmic muons. This apparatus has been designed as a real-size prototype to inspect containers using the muon tomography technique, i.e. by measuring the deflection of muons when traversing high-Z materials. The detection setup is based on eight position-sensitive X-Y planes, four placed below and four above the volume to be inspected, with good tracking capabilities for charged particles. The detection planes are segmented into strips of extruded plastic scintillators with WLS fibres to transport the light produced in the scintillator material to the photo-sensors (SiPMs) at one of the fibre ends. Detailed GEANT4 simulations have been carried out under different scenarios to investigate the response of the apparatus. The tomographic images are reconstructed by tracking algorithms and suitable imaging software tools. Simulations have demonstrated the possibility to reconstruct a 3D image of the volume to be inspected in a reasonable amount of time, compatible with the requirement of a fast inspection technique. The first two of the 48 detection modules are presently under construction.

UVSiPM is a light detector designed to measure the intensity of electromagnetic radiation in the 320-900 nm wavelength range. It has been developed in the framework of the ASTRI project whose main goal is the design and construction of an end-to-end Small Size class Telescope prototype for the Cherenkov Telescope Array. The UVSiPM instrument is composed by a multipixel Silicon Photo-Multiplier detector unit coupled to an electronic chain working in single photon counting mode with 10 nanosecond double pulse resolution, and by a disk emulator interface card for computer connection. The detector unit of UVSiPM is of the same kind as the ones forming the camera at the focal plane of the ASTRI prototype. Eventually, the UVSiPM instrument can be equipped with a collimator to regulate its angular aperture. UVSiPM, with its peculiar characteristics, will permit to perform several measurements both in lab and on field, allowing the absolute calibration of the ASTRI prototype., Comment: Accepted for publication in Nuclear Physics B (Proceedings Supplements)

The design and realization of a prototype for the Small-Size class Telescopes of the Cherenkov Telescope Array is one of the cornerstones of the ASTRI project. The prototype will adopt a focal plane camera based on Silicon Photo-Multiplier sensors that coupled with a dual mirror optics configuration represents an innovative solution for the detection of Atmospheric Cherenkov light. These detectors can be read by the Extended Analogue Silicon Photo-Multiplier Integrated Read Out Chip (EASIROC) equipped with 32-channels. In this paper, we report some preliminary results on measurements aimed to evaluate EASIROC capability of autotriggering and measurements of the trigger time walk, jitter, DAC linearity and trigger efficiency vs the injected charge. Moreover, the dynamic range of the ASIC is also reported., Comment: 4 pages, 8 figures, Proceedings of SciNeGHE 2012-9th Workshop on Science with the New Generation of High Energy Gamma-ray Experiments From high energy gamma sources to cosmic rays, one century after their discovery

In many fields and in particular in astrophysical observations, a chronic problem is the photon-starving condition, which becomes severe when images are to be obtained in short acquisition times (from micro to milliseconds), as happens in hot areas of astrophysics: optical counterparts of high-energy gamma-ray bursts, study and interpretation of Supernovae bursts. CCDs are inherently unable to provide accurate measurements of such fast low-intensity transients at high frame rates. To respond to single photons, suitable detectors must provide output signals that are sufficiently high to be individually processed by electronic circuits. Therefore, only detectors with an internal mechanism that provides a high multiplication of charge carriers are suitable, namely vacuum tube photomultipliers (PMTs), solid-state avalanche photodiodes (APDs) and electron-multiplying CCDs (EMCCDs). In PMTs, the photocathodes available for the visible spectral range provide fairly good quantum efficiency and low noise, whereas cathodes for the red and near-infrared range have lower quantum efficiency and must be cooled to reduce the dark-count rate. PMTs are bulky, and so not suitable for assembly in large arrays, fragile, sensitive to electromagnetic disturbances and mechanical vibrations, require high supply voltages (1–2 kV) and are costly devices, particularly the high-performance models. EM-CCDs exploit an internal multiplication process to achieve sub-electron readout noise, thus being able to detect single photons. Their quantum efficiency is very high, and they are inherently suited to imaging applications. However, due to their readout technique, they cannot provide frame rates higher than a few kilo-frames per second, and cannot be used in extreme timeresolved measurements. Single photons can be detected efficiently by avalanche diodes operating in Geiger mode, known as Single-Photon Avalanche Diodes (SPADs). Avalanche photodiodes have the typical advantages of solid state devices (small size, low bias voltage, low power consumption, ruggedness and reliability, suited to building integrated systems). In the last few years, a new kind of planar semiconductor device has slowly but steadily come out, namely the silicon photomultiplier (SiPM), with promising features that, in some respect, could even replace traditional photomultiplier tubes (Kovaltchouk et al, 2005). Based on a Geiger mode avalanche photodiode elementary cell, it consists of an array of n

Iqueye is a single photon counting very high speed photometer built for the ESO 3.5m New Technology Telescope (NTT) in La Silla (Chile) as prototype of a 'quantum' photometer for the 42m European Extremely Large Telescope (E-ELT). The optics of Iqueye splits the telescope pupil into four portions, each feeding a Single Photon Avalanche Diode (SPAD) operated in Geiger mode. The SPADs sensitive area has a diameter of 100 ?m, with a quantum efficiency better than 55% at 500 nm, and a dark count less than 50 Hz. The quenching circuit and temperature control are integrated in each module. A time-to-digital converter (TDC) board, controlled by a rubidium oscillator plus a GPS receiver, time tags the pulses from the 4 channels. The individual times are stored in a 2 TeraByte memory. Iqueye can run continuously for hours, handling count rates up to 8 MHz, with a final absolute accuracy of each time tag better that 0.5 ns. A first very successful run was performed in Jan 2009; both very faint and very bright stars were observed, demonstrating the high photometric quality of the instrument. The first run allowed also to identify some opto-mechanical improvements, which have been implemented for a second run performed in Dec 2009. The present paper will describe the first version, the improvements implemented in the second one, and some of the obtained astronomical results. © 2010 Copyright SPIE - The International Society for Optical Engineering.

In this contribution we present the results of the first morphological and electro-optical characterization of Silicon Photomultipliers (SiPM) for nuclear medical imaging applications fabricated in standard silicon planar technology at the STMicroelectronics Catania R&D clean room facility. We have improved our previous Geiger Mode Avalanche Photodiodes (GMAP) technology in order to realize a photodetector with relevant features in terms of single-photoelectron resolution, timing and photon detection efficiency. The performances of our devices, investigated in several experimental conditions and here reported make ST-SiPM suitable in many applications like for example PET (Positron Emission Tomography). Keywords: single photon counting, positron emission tomography, silicon photomultiplier, single photon avalanche photodiode, quenching resistor. 1. INTRODUCTION Photon counting techniques have been developed over many years by exploiting the remarkable performances of photomultiplier tubes (PMT) and avalanche photodiodes (APD) [1]. In r ecent years, a new kind of planar semiconductor photodetector, called Silicon PhotoMultiplier (SiPM), has been developed to detect single optical photons as a possible alternative to PMT and APD. SiPM have many advantages in terms of very fast timing response, high gain at low bias voltage, small recovery time, high detection efficiency in all the visible range and single photon response. Low bias voltage, low power consumption, good temperature and voltage stability, insensitivity to magnetic fields, reliability, ruggedness, compactness, no excess light damage and long lif espan are other favorable characteristics of these devices [2]. Moreover the solid-state detector approach has the typical advantages of a planar process integration, therefore arrays with a large number of pixels working in Geiger Mode can be manufactured at low cost

Arrays of Single Photon Avalanche Detectors (SPAD) are considered today as a possible alternative to PMTs and other semiconductor devices in several applications, like physics research, bioluminescence, Positron Emission Tomography (PET) systems, etc. We have developed and characterized a first prototype array produced by STMicroelectronics in silicon planar technology and working at low voltage (30−40 V) in Geiger mode operation. The single cell structure (size down to 20 μm) and the geometrical arrangement give rise to appealing intrinsic characteristics of the device, such as photon detection efficiency, dark count map, cross-talk effects, timing and energy resolution. New prototypes are under construction with a higher number of pixels that have a common output signal to obtain a so-called SiPM (Silicon PhotoMultiplier) configuration.

A compact system for counting and time-tagging single photons is presented, based on a monolithic array sensor of 60 pixels able to detect single photons, namely the single-photon avalanche diode array (SPADA). First, the working principle and performance of the single-photon detector pixel is detailed, with particular attention paid to monolithic array integration. Then the electronics needed to quench each pixel after avalanche ignition, namely the active-quenching circuit (AQC) is discussed, since the features of this quenching electronics dramatically affect the operating conditions of the detector, hence its actual performance. The discussion then focuses on integration of the SPADA system into Astrophysics applications such as adaptive optics, fast-transient imaging and atmospheric layer sensing. The whole electronics necessary to control SPADA operating conditions and temperature is also described, together with the complete opto-mechanics used to focus the telescope pupil onto the detector. Finally, experimental results are reported.

Experiments in nuclear physics, biomedicine and astronomy often require pulse-counting electronics for large numbers of channels. This paper describes an event-counting system attached to 60 channels of an innovative monolithic array of single- photon avalanche diodes (SPADA) intended for astronomical use. The system can capture events with pulse-counting rates of up to 20 MHz, a minimum integration time of 10 mus, which results in a data acquisition rate of 100 000 frames per second. It can also store several hours' worth of data. This performance is achieved in a system that offers a high degree of flexibility, is small in size and has a low cost. The implementation is based on a commercial-off-the-shelf (COTS) single board, fitted with an FPGA and a DSP. This board is connected to a PC by means of an IEEE 1394 high-speed serial link which stores the collected data and functions as a TCP/IP server. The data acquisition parameters, as well as the collected data, can be accessed by means of a custom-designed interface running on a TCP/IP client. A proof-of-concept system has been assembled and some test stand results are presented and discussed.

Astrophysical studies require accurate, sensitive and fast detectors to detect faint sources with high variability. Recently an array of Single Photon Avalanche Diodes (SPAD), SPADA, has been developed. This array is suitable for competitive adaptive optics operations and fast transient image acquisition at a fraction of the current cost of imaging arrays. The fabricated solid-state photon counters are rugged, easily integrated with the optics, free from readout noise, and have very fast frame rates (> 10 kHz, for visible corrections) with nanosecond electronic gating. In this paper, the following are described: the development of silicon monolithic arrays of 60 photon-counters, the detection electronics (based on integrated active quenching circuits for each pixel of the array), the real-time data-processing board implemented into FPGA and some aspects of the mechanical housing.

In this paper we report the results relative to the design and fabrication of Single Photon Avalanche Detectors (SPAD) operating at low voltage in planar technology. These silicon sensors consist of pn junctions that are able to remain quiescent above the breakdown voltage until a photon is absorbed in the depletion volume. This event is detected through an avalanche current pulse. Device design and critical issues in the technology are discussed. Experimental test procedures are then described for dark-counting rate, afterpulsing probability, photon timing resolution, quantum detection efficiency. Through these experimental setups we have measured the electrical and optical performances of different SPAD technology generations. The results from these measurements indicate that in order to obtain low-noise detectors it is necessary to introduce a local gettering process and to realize the diode cathode through in situ doped polysilicon deposition. With such technology low noise detectors with dark counting rates at room temperature down to 10c/s for devices with 10mm diameter, down to 1kc/s for 50mm diameter have been obtained. Noticeable results have been obtained also as far as time jitter and quantum detection efficiency are concerned. This technology is suitable for monolithic integration of SPAD detectors and associated circuits. Small arrays have already been designed and fabricated. Preliminary results indicate that good dark count rate uniformity over the different array pixels has already been obtained.

This is a progress report on preliminary test measurements aimed to evaluate the performance of new Single Photon Avalanche Diodes (SPAD) developed by ST Microelectronics. Various samples with different dimensions (from 10 to 100 μm diameter) and two 5x5 arrays (20 and 40 μm) are manufactured by STM; some of which have been characterized. A brief description of the device and its main characteristics (dark, quantum efficiency and linearity) are presented.

We present the development of silicon monolithic arrays of 60 photon-counters (SPADA, Single-Photon Avalanche Diode Array) for the visible. The SPADA system is suitable for state-of-the-art Adaptive Optics operations and Fast Transient image acquisitions, at quite a fraction of the current cost of imaging arrays. The fabricated solid-state photon counters are rugged, easy to be integrated in the optical system. They are free from readout noise and provide very fast frame-rates (>10kHz, for visible corrections) and nanosecond electronic gating (for ranging the up-going laser beam). The detection head has been integrated into an optomechanical system suitable for alignment and focusing in available astrophysics telescopes. The detection electronics includes an integrated Active Quenching Circuits for each pixel of the array. The real-time data-processing board is implemented into FPGA and DSP and is configurable for dealing with different applications: the extraction of the curvature wavefront for AO applications, and the acquisition and processing of two-dimensional images with fast frame rate. A remote host computer controls all the SPADA blocks and uploads the processed information and images. We report the optical and electrical characterization of the detectors and the associated electronics.

A new type of position sensor (CMOS-APS) used as readout system in MCP-based intensified photon counter is presented. Thanks to CMOS technology, the pixel addressing and the readout circuits as well as the analogue-to-digital converters are integrated into the chip. These unique characteristics make the CMOS-APS a very compact, low power consumption, photon counting system. The more classical Photon Counting Intensified CCDs (PC-ICCD), the selected CMOS-APS, the driving and interface electronics based on Field Programmable Gate Array (FPGA), and the adopted algorithm to compute the center of the luminous spot on the MCP phosphor screen are described.