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 mm2 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)

InGaAs/InAlAs single photon avalanche diode for 1550 nm photons.

A single photon avalanche diode (SPAD) with an InGaAs absorption region, and an InAlAs avalanche region was designed and demonstrated to detect 1550 nm wavelength photons. The characterization included leakage current, dark count rate and single photon detection efficiency as functions of temperature from 210 to 294 K. The SPAD exhibited good temperature stability, with breakdown voltage dependence of approximately 45 mV K(-1). Operating at 210 K and in a gated mode, the SPAD achieved a photon detection probability of 26% at 1550 nm with a dark count rate of 1 × 10(8) Hz. The time response of the SPAD showed decreasing timing jitter (full width at half maximum) with increasing overbias voltage, with 70 ps being the smallest timing jitter measured

"Delirium Day": A nationwide point prevalence study of delirium in older hospitalized patients using an easy standardized diagnostic tool

Background: To date, delirium prevalence in adult acute hospital populations has been estimated generally from pooled findings of single-center studies and/or among specific patient populations. Furthermore, the number of participants in these studies has not exceeded a few hundred. To overcome these limitations, we have determined, in a multicenter study, the prevalence of delirium over a single day among a large population of patients admitted to acute and rehabilitation hospital wards in Italy. Methods: This is a point prevalence study (called "Delirium Day") including 1867 older patients (aged 65 years or more) across 108 acute and 12 rehabilitation wards in Italian hospitals. Delirium was assessed on the same day in all patients using the 4AT, a validated and briefly administered tool which does not require training. We also collected data regarding motoric subtypes of delirium, functional and nutritional status, dementia, comorbidity, medications, feeding tubes, peripheral venous and urinary catheters, and physical restraints. Results: The mean sample age was 82.0 \ub1 7.5 years (58 % female). Overall, 429 patients (22.9 %) had delirium. Hypoactive was the commonest subtype (132/344 patients, 38.5 %), followed by mixed, hyperactive, and nonmotoric delirium. The prevalence was highest in Neurology (28.5 %) and Geriatrics (24.7 %), lowest in Rehabilitation (14.0 %), and intermediate in Orthopedic (20.6 %) and Internal Medicine wards (21.4 %). In a multivariable logistic regression, age (odds ratio [OR] 1.03, 95 % confidence interval [CI] 1.01-1.05), Activities of Daily Living dependence (OR 1.19, 95 % CI 1.12-1.27), dementia (OR 3.25, 95 % CI 2.41-4.38), malnutrition (OR 2.01, 95 % CI 1.29-3.14), and use of antipsychotics (OR 2.03, 95 % CI 1.45-2.82), feeding tubes (OR 2.51, 95 % CI 1.11-5.66), peripheral venous catheters (OR 1.41, 95 % CI 1.06-1.87), urinary catheters (OR 1.73, 95 % CI 1.30-2.29), and physical restraints (OR 1.84, 95 % CI 1.40-2.40) were associated with delirium. Admission to Neurology wards was also associated with delirium (OR 2.00, 95 % CI 1.29-3.14), while admission to other settings was not. Conclusions: Delirium occurred in more than one out of five patients in acute and rehabilitation hospital wards. Prevalence was highest in Neurology and lowest in Rehabilitation divisions. The "Delirium Day" project might become a useful method to assess delirium across hospital settings and a benchmarking platform for future surveys

High Detection Rate Fast-Gated CMOS Single-Photon Avalanche Diode Module

We present a novel instrument for fast-gated operation of a 50 μm CMOS SPAD (Complementary Metal-Oxide-Semiconductor Single-Photon Avalanche Diode), driven by an integrated fast-gated active quenching circuit with transition times faster than 300 ps (20-80%). The instrument is based on a custom system-in-package where the SPAD and its driving electronics are housed in a TO-8 package. The detector can be operated at repetition rates up to 160 MHz, with gate on-times as short as 500 ps, always guaranteeing a temporal response with 60 ps (FWHM) timing jitter and short exponential decay (53 ps time-constant). A dark-count rate as low as 1 cps is achieved operating the CMOS SPAD at 5 V above breakdown at a temperature of 263 K, still keeping the afterpulsing probability lower than 2%, with only 50 ns hold-off time, thanks to the fast-gating driving electronics. The instrument is housed in a compact 5 × 4 × 8 cm3 case and can be triggered by either an external or internal source. A USB link allows to adjust measurement parameters, SPAD bias voltage and operating temperature. The high re-configurability of the instrument and its state-of-the-art performance make it suitable for applications where high detection rates and low timing jitter are required

High count rate InGaAs/InP SPAD system with balanced SPAD-dummy approach running up to 1.4 GHz

The capability to achieve high count rates has become an imperative in the most areas where near-infrared single-photon counters are required to detect photons up to 1.7 mu m. Hence, afterpulsing mitigation is a dominant theme in recent works concerning systems based on InGaAs/InP SPADs. Given the challenges inherent in reducing the density of defects that give rise to the carrier trapping events causing afterpulsing, the only viable approach is to reduce the potential number of carriers that can be trapped by limiting the charge flow per avalanche event.In this paper we present a sine-wave gating system based on the balanced detector configuration. The gate frequency is programmable in a wide range (1.0 - 1.6 GHz) for allowing synchronization with an external laser system and for exploring the best trade-off between afterpulsing and photon detection efficiency. The long-term stability can be achieved with a stable cancelation of the gate feedthrough. In this work this is guaranteed by a feedback loop that continuously monitors the residual output power at the gate frequency and adjusts the amplitude and phase of the two sinusoids fed to the SPAD-dummy couple

Low-Noise, Low-Jitter, High Detection Efficiency InGaAs/InP Single-Photon Avalanche Diode

We present the performance of a novel InGaAs/InP single-photon avalanche diode (SPAD) with high detection efficiency and low noise thanks to the improvement of Zinc diffusion conditions and the optimization of the vertical structure. The 25-μm active-area diameter detector, operated in gated-mode with ON time of tens of nanoseconds, shows very low dark count rate (few kilo-counts per second at 225 K and 5 V of excess bias), 30% photon detection efficiency at 1550 nm, low afterpulsing, and a timing response with less than 90-ps full-width at half maximum and very fast exponential tail (time constant 60 ps). Therefore, this InGaAs/InP SPAD is among the best ones ever reported in the literature

0.16 μm BCD single-photon avalanche diode with 30 ps timing jitter, high detection efficiency and low noise

CMOS SPADs are nowadays an established imaging technology for applications requiring single-photon sensitivity in a compact form-factor (e.g. three-dimensional LIDAR imaging and fluorescence lifetime FLIM microscopy). However, we aimed at further enhance overall SPAD performances, by exploiting smart power technologies, such as the BCD (Bipolar-CMOS-DMOS) one. We achieved the present state-of-the-art SPADs fabricated in the 0.16 mu m BCD technology by STMicroelectronics, attaining >60% photon detection efficiency at 500 nm, dark count rate density <0.2 cps/mu m(2), and less than 30 ps FWHM timing jitter