Photon counting strategies with low-light-level CCDs

Abstract

Low light level charge‐coupled devices (L3CCDs) have recently been developed, incorporating on‐chip gain. They may be operated to give an effective readout noise of much less than one electron by implementing an on‐chip gain process allowing the detection of individual photons. However, the gain mechanism is stochastic and so introduces significant extra noise into the system. In this paper we examine how best to process the output signal from an L3CCD so as to minimize the contribution of stochastic noise, while still maintaining photometric accuracy. We achieve this by optimizing a transfer function that translates the digitized output signal levels from the L3CCD into a value approximating the photon input as closely as possible by applying thresholding techniques. We identify several thresholding strategies and quantify their impact on the photon counting accuracy and the effective signal‐to‐noise ratio. We find that it is possible to eliminate the noise introduced by the gain process at the lowest light levels. Reduced improvements are achieved as the light level increases up to about 20 photon pixel−1 and above this there is negligible improvement. Operating L3CCDs at very high speeds will keep the photon flux low, giving the best improvements in signal‐to‐noise ratio.

Development of new photon-counting detectors for single-molecule fluorescence microscopy

“…As a reminder, because of readout noise, very high theoretical frame rates are in practice useless for single-molecule detection owing to their low emitted signal. In other words, as soon as the readout rate reaches a value for which each pixel collects at most a few photons per frame, readout noise (or the effective noise factor associated with gain) will result in SNR too low for practical use, unless strategies equivalent to using these detectors as photon-counting detectors are used [136].…”

Spectral Subtraction: A New Approach to Remove Low‐ and High‐Order Speckle Noise

“…Such a strategy was discussed by Fowler & Gatley (1990) for the infrared imaging where the read-out is the dominant source of noise. Currently, ''zero-read noise'' photon counting detectors (Graham et al 2004;Basden et al 2003) are being developed for the direct detection of extrasolar planets. Furthermore, since the read noise is independent of the exposure time, increasing the overall exposure time could efficiently increase the S/ N.…”

Bayesian photon counting with electron-multiplying charge coupled devices (EMCCDs)

“…The advent of the EMCCD has inspired other authors to develop methods for photon counting, based on thresholding and multithresholding (Lantz et al 2008;Basden et al , 2003. Considering that an EMCCD has a limited dynamical range and negligible readout noise, one would typically apply an EMCCD in such a way that multiple images of the same object are available; as, for instance, in lucky imaging.…”