publications
Knowledge only real when shared. A selection of my favourite research publications as journal papers or conference proceedings.
2025
- Opt. Expr.Pile-up free fluorescence lifetime imaging with a SPAD-based single pixel cameraSerena Farina, Alberto Ghezzi, Ivan Labanca, Giulia Acconcia, Cosimo D’Andrea, Andrea Farina, and Ivan RechOptics Express, 2025
In the last years, single-pixel imaging (SPI) has been extensively utilized in fluorescence lifetime imaging (FLIM) experiments. In this context, to attain high temporal resolution, time-correlated single photon counting (TCSPC) is typically adopted, with the major drawback of the pile-up phenomenon, that limits the photon count rate to 1–5% of the laser excitation rate. This clearly hinders the possibility of monitoring a wide variety of biological phenomena in real-time. In this paper, to the best of our knowledge, we apply for the first time to a single-pixel camera (SPC) a hardware-based method, that allows to completely avoid the onset of pile-up by matching the dead time of the employed single-photon avalanche diode (SPAD) detector to an integer multiple of the laser period. We therefore demonstrate that undistorted and high-fidelity lifetime maps can be acquired at count rates (40%) well above the classic pile-up limitation, even in the presence of computational imaging algorithms. These results are supported by a thorough analysis of both the raw data prior to the reconstruction process and the final reconstructed lifetime maps.
@article{farina2025pile, title = {Pile-up free fluorescence lifetime imaging with a SPAD-based single pixel camera}, author = {Farina, Serena and Ghezzi, Alberto and Labanca, Ivan and Acconcia, Giulia and D'Andrea, Cosimo and Farina, Andrea and Rech, Ivan}, journal = {Optics Express}, volume = {33}, number = {11}, pages = {22296--22307}, year = {2025}, publisher = {Optica Publishing Group}, doi = {10.1364/OE.555297} } - Microchannel plate based photon counting at UV wavelengths for astronomy applicationsSerena Farina, Michela Uslenghi, Giorgio Toso, Luca Schettini, Mauro Fiorini, Salvatore Incorvaia, Leonardo Nassi, Adele Ciavarella-Ciavarella, Giacomo Borghi, Marco Carminati, and othersIn Quantum Optics and Photon Counting 2025, 2025
Photon counting in the far and extreme ultraviolet (FUV and EUV from 40 to 200 nm) is an important technique in various astronomic fields, such as solar physics, planetary atmosphere and surface, stellar formation and galaxies evolution studies. Thanks to their solar blindness, good efficiency at UV wavelengths and low dark count rates, microchannel plates (MCPs) are typically utilized to build imaging and spectroscopic space-based astronomical instruments. In this framework, the major limitations of microchannel plates are represented by limited dynamic range and lifetime. Both parameters can benefit from the use of ALD-MCPs and the ability to operate the MCP at low gain. However, this requires the development of new readout systems that do not themselves limit the system’s performance. To fully leverage the properties of the new MCPs, operating them at low gain, we have proposed to couple the MCP to a custom readout circuit, composed of a bi-dimensional anode matrix with a pitch of 35 µm; each pixel features a charge acquisition and discriminating chain with an extremely low readout noise. This allows attaining single-photon detection together with a high-dynamic range up to 100 kcps per pixel and a high spatial resolution. A first prototype of the detector with a 32x32 readout circuit has been developed and assembled in an ultra-high vacuum custom chamber. The first measurements demonstrate good spatial resolution and linearity; further tests are currently being performed to fully characterize the detector performance. Future works envision instead a possible extension of the prototype to a higher dimension matrix to cover the whole active area of the MCP.
@inproceedings{farina2025microchannel, title = {Microchannel plate based photon counting at UV wavelengths for astronomy applications}, author = {Farina, Serena and Uslenghi, Michela and Toso, Giorgio and Schettini, Luca and Fiorini, Mauro and Incorvaia, Salvatore and Nassi, Leonardo and Ciavarella-Ciavarella, Adele and Borghi, Giacomo and Carminati, Marco and others}, booktitle = {Quantum Optics and Photon Counting 2025}, volume = {13525}, pages = {59--64}, year = {2025}, organization = {SPIE}, doi = {10.1117/12.3058225} }
2024
- Characterization of the dark signal of the Solar Orbiter/Metis detectorsM. Uslenghi, L. Teriaca, K. Heerlein, G. Nicolini, M. Pancrazzi, M. Romoli, Serena Farina, L. Abbo, A. Burtovoi, C. Casini, Y. De Leo, F. Frassati, G. Jerse, F. Landini, G Russano, C. Sasso, and R. SusinoIn X-Ray, Optical, and Infrared Detectors for Astronomy XI, 2024
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.
@inproceedings{uslenghi2024characterization, title = {Characterization of the dark signal of the Solar Orbiter/Metis detectors}, author = {Uslenghi, M. and Teriaca, L. and Heerlein, K. and Nicolini, G. and Pancrazzi, M. and Romoli, M. and Farina, Serena and Abbo, L. and Burtovoi, A. and Casini, C. and De Leo, Y. and Frassati, F. and Jerse, G. and Landini, F. and Russano, G and Sasso, C. and Susino, R.}, booktitle = {X-Ray, Optical, and Infrared Detectors for Astronomy XI}, volume = {13103}, pages = {817--828}, year = {2024}, organization = {SPIE}, doi = {10.1117/12.3028609} }
2023
- A 1.9 ps-rms precision time-to-amplitude converter with 782 fs lsb and 0.79%-rms dnlGiulia Acconcia, Francesco Malanga, Serena Farina, Massimo Ghioni, and Ivan RechIEEE Transactions on Instrumentation and Measurement, 2023
Measuring a time interval in the nanoseconds range has opened the way to 3-D imaging, where additional information as distance of objects light detection and ranging (LiDAR) or lifetime decay fluorescence-lifetime imaging (FLIM) is added to spatial coordinates. One of the key elements of these systems is the time measurement circuit, which encodes a time interval into digital words. Nowadays, most demanding applications, especially in the biological field, require time-conversion circuits with a challenging combination of performance, including sub-ps resolution, ps precision, several ns of measurement range, linearity better than few percent of the bin width (especially when complex lifetime data caused by multiple factors have to be retrieved), and operating rates in the order of tens of Mcps. In this article, we present a time-to-amplitude converter (TAC) implemented in a SiGe 350 nm process featuring a resolution of 782 fs, a minimum timing jitter as low as 1.9 ps-rms, a DNL down to 0.79% LSB-rms, and conversion rate as high as 12.3 Mcps. With an area occupation of 0.2 mm2 [without PADs and digital-to-analog converter (DAC)], a FSR up to 100 ns, and a power dissipation of 70 mW, we developed a circuit suitable to be the core element of a densely integrated, faster and high-performance system.
@article{acconcia20231, title = {A 1.9 ps-rms precision time-to-amplitude converter with 782 fs lsb and 0.79\%-rms dnl}, author = {Acconcia, Giulia and Malanga, Francesco and Farina, Serena and Ghioni, Massimo and Rech, Ivan}, journal = {IEEE Transactions on Instrumentation and Measurement}, volume = {72}, pages = {1--11}, year = {2023}, publisher = {IEEE}, doi = {10.1109/TIM.2023.3271755} } - A 4.5 ps precision TCSPC system: design principles and characterizationSerena Farina, Ivan Labanca, Giulia Acconcia, and Ivan RechIEEE Journal of Selected Topics in Quantum Electronics, 2023
With 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.
@article{farina20234, title = {A 4.5 ps precision TCSPC system: design principles and characterization}, author = {Farina, Serena and Labanca, Ivan and Acconcia, Giulia and Rech, Ivan}, journal = {IEEE Journal of Selected Topics in Quantum Electronics}, year = {2023}, publisher = {IEEE}, doi = {10.1109/JSTQE.2023.3316601} }
2022
- 10-nanosecond dead time and low afterpulsing with a free-running reach-through single-photon avalanche diodeSerena Farina, Ivan Labanca, Giulia Acconcia, Massimo Ghioni, and Ivan RechReview of Scientific Instruments, 2022
The reduction of detector dead time represents an enabling factor in several photon counting applications. In this work, we investigate the free-running operation of reach-through single-photon avalanche diodes (SPADs) at ultra-low dead times. By employing a fast active quenching circuit with direct bonding to the detector, we are able to achieve a 10 ns dead time with a thick SPAD by Excelitas, still maintaining extremely low afterpulsing probabilities (below 1.5%).
@article{farina202210, title = {10-nanosecond dead time and low afterpulsing with a free-running reach-through single-photon avalanche diode}, author = {Farina, Serena and Labanca, Ivan and Acconcia, Giulia and Ghioni, Massimo and Rech, Ivan}, journal = {Review of Scientific Instruments}, volume = {93}, number = {5}, year = {2022}, publisher = {AIP Publishing}, doi = {10.1063/5.0086312} } - Versatile multichannel time-to-amplitude converter for high-speed and high-precision timing applicationsFrancesco Malanga, Giulia Acconcia, Serena Farina, Massimo Ghioni, and Ivan RechIn Advanced Photon Counting Techniques XVI, 2022
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.
@inproceedings{malanga2022versatile, title = {Versatile multichannel time-to-amplitude converter for high-speed and high-precision timing applications}, author = {Malanga, Francesco and Acconcia, Giulia and Farina, Serena and Ghioni, Massimo and Rech, Ivan}, booktitle = {Advanced Photon Counting Techniques XVI}, pages = {PC120890C}, year = {2022}, organization = {SPIE}, doi = {10.1117/12.2618501} }
2021
- Toward ultra-fast time-correlated single-photon counting: A compact module to surpass the pile-up limitSerena Farina, Giulia Acconcia, Ivan Labanca, Massimo Ghioni, and Ivan RechReview of Scientific Instruments, 2021
Time-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.
@article{farina2021toward, title = {Toward ultra-fast time-correlated single-photon counting: A compact module to surpass the pile-up limit}, author = {Farina, Serena and Acconcia, Giulia and Labanca, Ivan and Ghioni, Massimo and Rech, Ivan}, journal = {Review of Scientific Instruments}, volume = {92}, number = {6}, year = {2021}, publisher = {AIP Publishing}, doi = {10.1063/5.0044774} } - Above pile-up fluorescence microscopy with a 32 Mc/s single-channel time-resolved SPAD systemSerena Farina, Ivan Labanca, Giulia Acconcia, Alberto Ghezzi, Andrea Farina, Cosimo D’Andrea, and Ivan RechOptics Letters, 2021
One of the major drawbacks of time-correlated single-photon counting (TCSPC) is generally represented by pile-up distortion, which strongly bounds the maximum acquisition speed to a few percent of the laser excitation rate. Based on a previous theoretical analysis, recently we presented the first, to the best of our knowledge, low-distortion and high-speed TCSPC system capable of overcoming the pile-up limitation by perfectly matching the single-photon avalanche diode (SPAD) dead time to the laser period. In this work, we validate the proposed system in a standard fluorescence measurement by comparing experimental data with the reference theoretical framework. As a result, a count rate of 32 Mc/s was achieved with a single-channel system still observing a negligible lifetime distortion.
@article{farina2021above, title = {Above pile-up fluorescence microscopy with a 32 Mc/s single-channel time-resolved SPAD system}, author = {Farina, Serena and Labanca, Ivan and Acconcia, Giulia and Ghezzi, Alberto and Farina, Andrea and D’Andrea, Cosimo and Rech, Ivan}, journal = {Optics Letters}, volume = {47}, number = {1}, pages = {82--85}, year = {2021}, publisher = {Optica Publishing Group}, doi = {10.1364/OL.444815} }