Davide Contini

Afterpulse-like noise limits dynamic range in time-gated applications of thin-junction silicon single-photon avalanche diode

We describe a source of noise in thin-junction silicon single-photon avalanche diode arising after strong illumination either during the ON (voltage above breakdown) or the OFF (voltage below breakdown) time. It increases the background noise with respect to primary dark count rate similarly to the afterpulsing process, but it is not related to a previous detector ignition. The amount of noise is linearly dependent on the power of light impinging on the detector and time constants are independent of the electric field. This phenomenon is the main limiting factor for the dynamic-range during time-gated measurements in condition of strong illumination.

Time-resolved single-photon detection module based on silicon photomultiplier: A novel building block for time-correlated measurement systems

We present the design and preliminary characterization of the first detection module based on Silicon Photomultiplier (SiPM) tailored for single-photon timing applications. The aim of this work is to demonstrate, thanks to the design of a suitable module, the possibility to easily exploit SiPM in many applications as an interesting detector featuring large active area, similarly to photomultipliers tubes, but keeping the advantages of solid state detectors (high quantum efficiency, low cost, compactness, robustness, low bias voltage, and insensitiveness to magnetic field). The module integrates a cooled SiPM with a total photosensitive area of 1 mm(2) together with the suitable avalanche signal read-out circuit, the signal conditioning, the biasing electronics, and a Peltier cooler driver for thermal stabilization. It is able to extract the single-photon timing information with resolution better than 100 ps full-width at half maximum. We verified the effective stabilization in response to external thermal perturbations, thus proving the complete insensitivity of the module to environment temperature variations, which represents a fundamental parameter to profitably use the instrument for real-field applications. We also characterized the single-photon timing resolution, the background noise due to both primary dark count generation and afterpulsing, the single-photon detection efficiency, and the instrument response function shape. The proposed module can become a reliable and cost-effective building block for time-correlated single-photon counting instruments in applications requiring high collection capability of isotropic light and detection efficiency (e.g., fluorescence decay measurements or time-domain diffuse optics systems).

Fast-gated SPAD for ultra-wide dynamic range optical investigations

We describe the performances of a fast-gated single-photon avalanche diode for biomedical optical investigations. A dynamic range of 8 orders of magnitude is obtained in few minutes measurement time.

Non-contact time-domain imaging of functional brain activation and heterogeneity of superficial signals

Non-contact scanning at small source-detector separation enables imaging of cerebral and extracranial signals at high spatial resolution and their separation based on early and late photons accounting for the related spatio-temporal characteristics.

Tomography of brain activation using a time-gated camera

We propose a system for 3D tomography using a single pulsed source and a time-gated camera for functional imaging studies. Reconstructions were based on a linear model based on small perturbation assumption, applying Tikhonov regularization. This approach was tested against simulations, demonstrating both detection and localization capabilities. Preliminary measurements on realistic inhomogeneous phantoms showed good detection sensibility, even for a low optical contrast, but poorer localization properties, possibly due to the still low SNR of the system. Finally, an initial in vivo test on a motor cortex activation paradigm is presented.