Single-photon Sensitive Light-in-fight Imaging
Single-photon may refer to: * Photon counting devices capable of counting individual photons, for example: ** Superconducting nanowire single-photon detectors ** Single-photon avalanche diodes, a class of solid-state photodetectors * Single-photon sources * Single-photon emission computed tomography Single-photon emission computed tomography (SPECT, or less commonly, SPET) is a nuclear medicine tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera (that is, ...

Photon Counting
Photon counting is a technique in which individual photons are counted using a single-photon detector (SPD). A single-photon detector emits a pulse of signal for each detected photon, in contrast to a normal photodetector, which generates an analog signal proportional to the photon flux. The number of pulses (but not their amplitude) is counted, giving an integer number of photons detected per measurement interval. The counting efficiency is determined by the quantum efficiency and the system's electronic losses. Many photodetectors can be configured to detect individual photons, each with relative advantages and disadvantages. Common types include photomultipliers, geiger counters, single-photon avalanche diodes, superconducting nanowire single-photon detectors, transition edge sensors, and scintillation counters. Charge-coupled devices can be used. Advantages Photon counting eliminates gain noise, where the proportionality constant between analog signal out and number of p ...
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Superconducting Nanowire Single-photon Detector
The superconducting nanowire single-photon detector (SNSPD or SSPD) is a type of optical and near-infrared single-photon detector based on a current-biased superconducting nanowire. It was first developed by scientists at Moscow State Pedagogical University and at the University of Rochester in 2001. The first fully operational prototype was demonstrated in 2005 by the National Institute of Standards and Technology (Boulder), and BBN Technologies as part of the DARPA Quantum Network. As of 2021, a superconducting nanowire single-photon detector is the fastest single-photon detector (SPD) for photon counting. It is a key enabling technology for quantum optics and optical quantum technologies. SNSPDs are available with very high detection efficiency, very low dark count rate and very low timing jitter, compared to other types of single-photon detectors. As of 2021, commercial SNSPD devices are available in multichannel systems in a price range of 100,000 euros. Principle of op ...
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Single-photon Avalanche Diode
A single-photon avalanche diode (SPAD) is a solid-state photodetector within the same family as photodiodes and avalanche photodiodes (APDs), while also being fundamentally linked with basic diode behaviours. As with photodiodes and APDs, a SPAD is based around a semi-conductor p-n junction that can be illuminated with ionizing radiation such as gamma, x-rays, beta and alpha particles along with a wide portion of the electromagnetic spectrum from ultraviolet (UV) through the visible wavelengths and into the infrared (IR). In a photodiode, with a low reverse bias voltage, the leakage current changes linearly with absorption of photons, i.e. the liberation of current carriers (electrons and/or holes) due to the internal photoelectric effect. However, in a SPAD, the reverse bias is so high that a phenomenon called impact ionisation occurs which is able to cause an avalanche current to develop. Simply, a photo-generated carrier is accelerated by the electric field in the devic ...
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Single-photon Source
Single-photon sources are light sources that emit light as single particles or photons. These sources are distinct from coherent light sources (lasers) and thermal light sources such as incandescent light bulbs. The Heisenberg uncertainty principle dictates that a state with an exact number of photons of a single frequency cannot be created. However, Fock states (or number states) can be studied for a system where the electric field amplitude is distributed over a narrow bandwidth. In this context, a single-photon source gives rise to an effectively one-photon number state. Photons from an ideal single-photon source exhibit quantum mechanical characteristics. These characteristics include photon antibunching, so that the time between two successive photons is never less than some minimum value. This behaviour is normally demonstrated by using a beam splitter to direct about half of the incident photons toward one avalanche photodiode, and half toward a second. Pulses from one detec ...
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