Metis, one of the instruments of the ESA mission Solar Orbiter (launched on 10 February 2020, from Cape Canaveral), is a coronagraph with 2 channels, capable of performing broadband polarization imaging in the visible range (580 to 640nm), and narrow-band imaging in UV (HI Lyman-α 121.6nm). It is equipped with two detectors based on CMOS APS sensors: the visible channel includes a custom CMOS sensor with direct illumination, while the UV channel is provided with an intensified camera, based on a Star-1000 rad-hard CMOS APS coupled via a 2:1 fiber optic taper to a single-stage Microchannel Plate intensifier coated with an opaque KBr photocathode and sealed with an entrance MgF2 window. Dark subtraction is a crucial step in the data reduction pipeline, thus requiring careful in-flight monitoring and characterization of the dark signal. Since it is not possible to directly acquire dark images with the visible detector, as the door of the instrument is not light-tight, an ad hoc procedure has been designed to estimate the correction to be applied. In the case of the UV detector, however, it is possible to acquire dark frames by turning off the intensifier. Due to small fluctuations occurring on the bias signal level even on short timescales, an algorithm has been developed to correct the dark matrix frame by frame.
Microchannel plates-based detectors have been for a long time the detectors of choice for astronomical applications in the FUV/EUV, due to their photon counting capability and the possibility of solar blindness. In the framework of technological R&D for a future astronomical FUV/EUV spectrograph, we are developing a new readout system to allow unprecedented dynamic range. The goal is to realize a photon counting, solar blind, UV detector, based on a MCP read out with a 2D anode array integrated in a custom designed Read Out Integrated Circuit (MIRA: Microchannel plate Readout ASIC), able to reach unprecedented performance in terms of dynamic range combined with spatial resolution close to 30μm. Each pixel contains an anode to collect the electrons emitted by the MCP, a low noise amplifier and filter to maximize the SNR, a comparator to recognize and count single photon events, logic to correct for charge sharing among pixels (CSCL) and two counters. Some preliminary characterization of the first prototype, based on a demonstrator of the MIRA ASIC, 32×32 pixels, 35×35μm2 size, for a total chip area of 2×2mm2, integrated into a standard demountable MCP intensifier, have been carried out.
KEYWORDS: Picosecond phenomena, Time correlated single photon counting, Imaging systems, Analog to digital converters, Superconductors, Single photon avalanche diodes, Nanowires, Quantum systems, Quantum imaging
The constant advancements in single-photon technologies have led to the development of detectors with amazingly low jitter, that can play an important role in quantum measurements. A major limitation to their full exploitation in practical applications is represented by the timing electronics that should possess both low jitter characteristics, as well as good speed, linearity, and full-scale range (FSR) performance. In this paper, we propose a new TACbased single-channel timing system that features a state-of-the-art timing jitter of 4.5 ps FWHM, along with a peak-to-peak DNL of 1.5% LSB and a speed of 12 Mcps, over a wide full-scale range of 12.5 ns. Thanks to the promising results achieved in experiments with SNSPDs, we are extending the system to eight channels, to leverage converter parallelization to further reduce timing jitter below 2 ps.
Time-correlated single-photon counting (TCSPC) allows to achieve picosecond-precision measurements for low-light signals. However, TCSPC suffers from pile-up distortion, constraining the acquisition rate to 1-5% of the laser rate. To overcome the issue, our research focuses on high-rate TCSPC methodologies: in 2017 we reported a hardware acquisition approach, that has been translated into a real system, guaranteeing low distortion at 32 Mcps. This talk provides an overview on the research project, and in particular on the two validation campaigns carried out in fluorescence and lidar measurements, and on our first on-field experiment, i.e. the application of the technique to a single-pixel camera.
With the development of advanced and dedicated timing instrumentation, Time-Correlated Single-Photon Counting (TCSPC) has become the de-facto standard for the measurement of low-light signals in a wide variety of applications, from fluorescence observation in biology to 3D scanning in laser ranging. Despite the huge technical improvements, the historical pile-up limitation still represents an open issue, that reduces the maximum acquisition rate to few percent (1-5 %) of the laser excitation rate. This prevents high-speed and real-time exploitation of TCSPC, thus reducing the range of applications that can benefit from such a powerful technique. To overcome this limitation, in 2017 we proposed a novel theoretical approach based on a time-matching between detector dead time and laser period, and in 2021 we designed the first system implementing this new technique. Preliminary results showed a good accordance between the theoretical framework and practical experiments with standard fluorescence dies up to a rate of 32 Mcps. Since then, we have been working on the exploitation of our system in further practical measurements, to perform a deeper validation of its potential. In particular, we have explored the application of our system into a lidar experiment, as no a-priori knowledge is necessary on the specific type of signal. In this proceeding, we present an overview of our work from the theoretical principles to the field verification.
Multispectral fluorescence lifetime microscopy (FLIM) is a valuable tool for biomedical and environmental applications. A multidimensional acquisition scheme (space, time, spectrum) provides high information content and the drawback of long acquisition/processing times. Compressive Sensing (CS) combined with Single-Pixel Camera (SPC) acquisition scheme has been proposed as a strategy to reduce the number of measurements. We present a multispectral FLIM system based on SPC, CS and data fusion (DF) with a high-resolution camera to strongly reduce the acquisition time. We adopted a novel method for TCSPC to increase the count-rate. The system is characterized and validated on a cellular sample.
In this work, we present the configurable Fast-Time-to-Amplitude Converter (FTAC), a versatile and completely integrated multichannel timing device constituted by 8 high-performance Time-to-Amplitude Converters (TACs) and a smart front-end logic. The designed converter can not only provide state-of-the-art performance in terms of conversion frequency (up to 100Mcps) and timing precision (down to 1.1ps rms, i.e. 2.6 ps Full Width at Half Maximum), but also a unique flexibility to the end user, who can select the most suitable configuration for its specific requirements. Above all, this chip gives the possibility of using the 8 channels separately, as a building block of a multichannel system, or combining the internal converters to reach picosecond precision, that could open the way to on-field exploitation of Super Conducting Nanowire Single Photon Detectors (SNSPDs). The chip provides 11 different configurations among which select the best option in terms of a combination of parallel channels, speed and timing precision.
Time-Correlated Single Photon Counting (TCSPC) represents a fundamental tool for the investigation of biological light signals. Unfortunately, due to pile-up distortion the photon acquisition rate must be kept below few percents of the laser rate, thus increasing the acquisition time.
Recently, we proposed a single-channel TCSPC system allowing us to overcome pile-up by matching the detector dead time to the laser period. In this work, we perform on-field fluorescence measurements with this system showing that an acquisition speed of 32 Mcps can be reached without significant distortion. Thanks to the promising results, we are now developing a multi-channel module based on the same acquisition technique.
Timing measurements triggered by photo-detection are widely used in several different fields, such as Time-Correlated Single Photon Counting (TCSPC), Quantum Key Distribution (QKD) or Light Detection and Ranging (LiDAR) systems. All these applications have in common one essential element, i.e. the timing electronics, which aims at measuring the time interval between two instants and whose requirements strictly depend on the application-specific goal. In this work, we present a versatile and fully-integrated timing chip hosting eight high-performance Time-to-Amplitude Converters (TACs) integrated with a smart logic, providing to the end user a unique flexibility to select the most suitable configuration for its specific requirements.
Time-Correlated Single Photon Counting (TCSPC) is a time-resolved and ultrasensitive technique, that provides the analysis of optical pulses to a wide range of different applications both in the biological and chemical domain. Nevertheless, an ultimate constraint to this technique has been historically posed by pile-up distortion, that typically restricts the maximum acquisition speed to few percent of the laser excitation rate. To surpass this fundamental limitation, a novel theoretical solution has been reported in a previous paper: with a perfect matching between detector dead time and laser period, it is possible to achieve a high-speed measurement, still maintaining negligible distortion. In this work, we present the design, characterization and experimental validation of a single-channel TCSPC system that implements the proposed idea. The essential core of the system consists in a compact Detection Head featuring a finely tunable dead time, thanks to a fully-integrated front-end electronics coupled to a custom technology Single-Photon Avalanche Diode (SPAD). This module is providing a picosecond precision timing signal, that is then acquired and digitized by means of a Fast Time to Amplitude Converter (F-TAC) architecture, followed by a high-end Field Programmable Gate Array (FPGA). In order to validate the proposed technique, we carried out on-field fluorescence lifetime measurements employing the newly developed system. The experimental results show good accordance with the previous theoretical framework. It is therefore possible to achieve high acquisition speed (32 Mcps) with an almost null lifetime distortion, thus paving the way to new advanced TCSPC applications.
Time-Correlated Single Photon Counting (TCSPC) is generally recognized as a powerful tool for Fluorescence Lifetime Imaging (FLIM), thanks to its inherently high sensitivity and timing precision. Nevertheless, one of the major drawbacks of the technique is represented by the so-called pile-up distortion, that typically limits the acquisition rate to few percent of the laser stimulation rate. In recent years, an innovative methodology has been proposed to overcome this restriction: by matching the detector dead time to the laser period an average acquisition rate of 40 Mcps is achieved, along with negligible distortion. In this work, we present the first single-channel system that implements the new measurement technique. To this aim, two modules have been specifically developed to accommodate a custom-technology Single-Photon Avalanche Diode (SPAD) and its dedicated acquisition chain. On one hand, a compact Detection Module hosts both a fully-integrated Active Quenching Circuit (AQC) to provide a finely-tunable dead time and a differential Pick-Up Circuit (PUC) to extract a picosecond-precision timing signal. On the other hand, a Time Conversion module is intended to acquire the fast timing signal thanks to a mixed-architecture Fast Time to Amplitude Converter (F-TAC). The experimental characterization proved that the modules feature excellent performance both in terms of timing precision (55 ps FWHM) and Differential Nonlinearity (4 % LSB peak to peak) and we’re now ready to compare the new technique with the classic pile-up limited approach in a real application on field.
Time-correlated measurements by means of single photon counting have been historically subject to a speed-distortion tradeoff, mainly due to the so-called pile-up effect. Recently, a new theoretical solution has been proposed showing that such tradeoff can be overcome using a detector dead time matched to the excitation period. This result opens the way to unprecedented speed operation in Time Correlated Single Photon Counting combined with low distortion. To achieve this goal, dedicated electronics has to be designed on purpose. In this paper, we report on the design of the first module that implements the proposed solution. Based on the exploitation of a
high-performance Single Photon Avalanche Diode, the module features a fast full-integrated Active Quenching Circuit able to drive the sensor and a dummy cell with a finely tunable dead time as short as 12.5ns, a fully-differential avalanche current readout circuit providing the timing information with a jitter lower than 54ps and the logic circuitry that is needed to prevent distortion at high rates. The timing information is converted by a Fast-TAC providing picosecond timing and high linearity along with a count rate as high as 80Mcps..
Time Correlated Single Photon Counting (TCSPC) is a widely diffused technique used in scientific experiments requiring the analysis of optical pulses with high timing precision. One of the major limitations affecting this tool are distortion phenomena at high count rates happening due to pile-up. As a result, experiments must be carried out at a slower operating rate than the laser excitation frequency (1%-5%). It has been recently demonstrated that matching the detector dead time with the duration of the laser excitation period allows to overcome the aforementioned speed limitation, while still keeping distortion low. Theoretical results envision a speed improvement by almost an order of magnitude. In this work we present dedicated integrated electronics to implement the proposed idea. The selected detector for this design is a custom technology SPAD in order to achieve high performance. The SPAD is externally driven by an Active Quenching Circuit (AQC) that senses the avalanche current and provides a prompt quenching and reset of the detector. The AQC features a finely tunable dead time and a low reset time, two key aspects to achieve a very-low distortion regime and high efficiency. The detector electric signal is read out by a fully differential pick-up circuit, delivering a timing differential signal with picosecond precision and rejecting disturbances thanks to a dummy cell. A fast time-to-amplitude converter is used to measure the time of arrival of the photons with picoseconds precision and high linearity.
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