14 Facts About Shot noise

Shot noise or Poisson noise is a type of noise which can be modeled by a Poisson process.

Shot noise occurs in photon counting in optical devices, where shot noise is associated with the particle nature of light.

Shot noise exists because phenomena such as light and electric current consist of the movement of discrete 'packets'.

Concept of shot noise was first introduced in 1918 by Walter Schottky who studied fluctuations of current in vacuum tubes.

The magnitude of shot noise increases according to the square root of the expected number of events, such as the electric current or intensity of light.

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Since the standard deviation of shot noise is equal to the square root of the average number of events N, the signal-to-noise ratio is given by:.

However, shot noise is temperature and frequency independent, in contrast to Johnson–Nyquist noise, which is proportional to temperature, and flicker noise, with the spectral density decreasing with increasing frequency.

Shot noise is distinct from voltage and current fluctuations expected in thermal equilibrium; this occurs without any applied DC voltage or current flowing.

Since shot noise is a Poisson process due to the finite charge of an electron, one can compute the root mean square current fluctuations as being of a magnitude.

In optics, shot noise describes the fluctuations of the number of photons detected due to their occurrence independent of each other.

Shot noise is easily observable in the case of photomultipliers and avalanche photodiodes used in the Geiger mode, where individual photon detections are observed.

However the same Shot noise source is present with higher light intensities measured by any photo detector, and is directly measurable when it dominates the Shot noise of the subsequent electronic amplifier.

Shot noise of a coherent optical beam is a fundamental physical phenomenon, reflecting quantum fluctuations in the electromagnetic field.

However, shot noise itself is not a distinctive feature of quantised field and can be explained through semiclassical theory.