122 research outputs found
Note: Wide-operating-range control for thermoelectric coolers
No full textA new algorithm for controlling the temperature of a thermoelectric cooler is proposed. Unlike a classic proportional-integral-derivative (PID) control, which computes the bias voltage from the temperature error, the proposed algorithm exploits the linear relation that exists between the cold side's temperature and the amount of heat that is removed per unit time. Since this control is based on an existing linear relation, it is insensitive to changes in the operating point that are instead crucial in classic PID control of a non-linear system
A simple and flexible FPGA based autocorrelator for afterpulse characterization of single-photon detectors
No full textSingle Photon Avalanche Diodes (SPADs) are widely employed for photon counting and timing in a variety of scientific and industrial applications. However they are affected by the afterpulsing effect, which can significantly increase the effective dark count rate of the detector. Being correlated with previous photon pulses, afterpulses can cause sharp distortions in photon correlation experiments. In this paper we exploit autocorrelation to characterize the afterpulsing of SPADs. A FPGA based autocorrelator has been specifically designed to this purpose, featuring a lag-time range from 10ns to more than 10ms, covering a range well beyond the longest expected trapped carrier lifetime
Overcoming Pile-up Limitation in Fluorescence Lifetime Imaging
No full textWe present the first compact Time-Correlated Single-Photon Counting single-channel system, capable of overcoming the typical pile-up limitation of Fluorescence Lifetime Imaging. An ultra-fast acquisition is obtained (40 Mcps), along with excellent timing results and negligible distortion
Near-zero distortion in TCSPC at more than one photon per excitation period: experimental validation
No full textThe time-correlated single-photon counting (TCSPC) technique is widely renowned for its capability of reconstructing rapid and weak light signals with exceptional sensitivity and sub-picosecond timing resolution. Unfortunately, the speed of TCSPC has been historically severely limited to avoid a phenomenon known as pileup distortion. For this reason, the count rate of a classic TCSPC acquisition channel is kept below a few percent of the laser excitation rate (usually 17c-57c). In this work, we experimentally validate a novel, to our knowledge, TCSPC theory recently reported that effectively overcomes such a limitation and finally achieves high-speed operation without distortion. Exploiting a singlephoton avalanche diode (SPAD), in this paper we show how to acquire additional information about the status of the system at run time, and by combining it with the classic TCSPC data histogram, we report how a count rate of approximately 607c of the excitation frequency with near-zero distortion can indeed be achieved with a commercial system
A 4.5 ps precision TCSPC system: design principles and characterization
No full textWith the recent advancements in single-photon detectors, very low-jitter timing systems are required to fully exploit their performance in real applications. In this article, we present the design principles and experimental characterization of a single-channel time-correlated single-photon counting (TCSPC) system, that achieves a jitter down to 4.5 ps FWHM, a peak-to-peak differential nonlinearity of 1.5 % LSB and a count rate of 12 Mcps over a nanoseconds full-scale range. These results have been attained by minimizing the different jitter contributions that are introduced at various levels in the whole timing chain, still without trading them off with the other performance parameters. To the best of our knowledge, this work represents the state-of-the-art performance in case of a full-scale range as large as 12.5 ns
Conceiving and designing high-performance TCSPC systems for biological and quantum imaging
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Toward ultra-fast time-correlated single-photon counting: A compact module to surpass the pile-up limit
No full textTime-Correlated Single-Photon Counting (TCSPC) is an excellent technique used in a great variety of scientific experiments to acquire exceptionally fast and faint light signals. Above all, in Fluorescence Lifetime Imaging (FLIM), it is widely recognized as the gold standard to record sub-nanosecond transient phenomena with picosecond precision. Unfortunately, TCSPC has an intrinsic limitation: to avoid the so-called pile-up distortion, the experiments have been historically carried out, limiting the acquisition rate below 5% of the excitation frequency. In 2017, we demonstrated that such a limitation can be overcome if the detector dead time is exactly matched with the excitation period, thus paving the way to unprecedented speedup of FLIM measurements. In this paper, we present the first single-channel system that implements the novel proposed methodology to be used in modern TCSPC experimental setups. To achieve this goal, we designed a compact detection head, including a custom single-photon avalanche diode externally driven by a fully integrated Active Quenching Circuit (AQC), featuring a finely tunable dead time and a short reset time. The output timing signal is extracted by using a picosecond precision Pick-Up Circuit (PUC) and fed to a newly developed timing module consisting of a mixed-architecture Fast Time to Amplitude Converter (F-TAC) followed by high-performance Analog-to-Digital Converters (ADCs). Data are transmitted in real-time to a Personal Computer (PC) at USB 3.0 rate for specific and custom elaboration. Preliminary experimental results show that the new TCSPC system is suitable for implementing the proposed technique, achieving, indeed, high timing precision along with a count rate as high as 40 Mcps
32ps timing jitter with a fully integrated front end circuit and single photon avalanche diodes
No full textExcellent performance of custom technology SPAD detectors have been widely demonstrated in recent years. Low-jitter timing measurements with these detectors require front end electronics able to sense the avalanche current at a very low level when the multiplication process is still confined in a very small area around the photon absorption point. Best in class results (35 ps full width at half maximum) have been obtained with discrete circuits not suitable to be used in densely integrated systems of SPAD arrays required by modern demanding applications. A new fully integrated front end able to read out the avalanche current with a timing jitter as low as 32 ps and suitable to be exploited with SPAD arrays is presented
Fully integrated time-to-amplitude converter for multidimensional TCSPC applications
No full textOver the past years an always growing interest has arisen about the measurement technique of time-correlated single photon counting (TCSPC), since it allows the analysis of extremely fast and weak light waveforms with a picoseconds resolution. Consequently, many applications exploiting TCSPC have been developing in several fields such as medicine and chemistry. Moreover, the use of multianode PMT and of single photon avalanche diode arrays led to the development of multichannel acquisition systems, employed in even more applications. Since TCSPC basically consists of the measurement of the arrival time of a photon, a high resolution and high linearity time measurement block is of the utmost importance, and in order to realize multidimensional systems, it has to be integrated to reduce both cost and area. We have designed and fabricated a 4 channel fully integrated time-to-amplitude converter (TAC), built in 0.35 μm Si-Ge technology, characterized by a very good time resolution (less than 50 ps), low differential nonlinearity (better than 2% peak-peak and less than 0.1% rms), high counting rate (16 MHz), low and constant power dissipation (50 mW), and low area occupation (2.58x1.28 mm2). Moreover our measurements show a very little crosstalk between the converters integrated on the same chip; this feature together with low power and low area make the fabricated converter suitable for parallelization, so it can be the starting point for future large scale multi-channel acquisition chains
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