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The regimes are defined by the relationship between the variance and average number of photon counts for the corresponding distribution. Both Poissonian and super-Poissonian light can be described by a semi-classical theory in which the light source is modeled as an electromagnetic wave and the atom is modeled according to quantum mechanics.
Photon counting eliminates gain noise, where the proportionality constant between analog signal out and number of photons varies randomly. Thus, the excess noise factor of a photon-counting detector is unity, and the achievable signal-to-noise ratio for a fixed number of photons is generally higher than the same detector without photon counting.
The energy content of this volume element at 5 km from the station is 2.1 × 10 −10 × 0.109 = 2.3 × 10 −11 J, which amounts to 3.4 × 10 14 photons per (). Since 3.4 × 10 14 > 1, quantum effects do not play a role. The waves emitted by this station are well-described by the classical limit and quantum mechanics is not needed.
Quantitatively, the number of photons absorbed, between the points and + along the path of a beam is the product of the number of photons penetrating to depth times the number of absorbing molecules per unit volume times the absorption cross section :
There are two ways in which probability can be applied to the behavior of photons; probability can be used to calculate the probable number of photons in a particular state, or probability can be used to calculate the likelihood of a single photon to be in a particular state. The former interpretation violates energy conservation.
The daily light integral (DLI) is the number of photosynthetically active photons (photons in the PAR range) accumulated in a square meter over the course of a day. It is a function of photosynthetic light intensity and duration (day length) and is usually expressed as moles of light (mol photons) per square meter (m −2) per day (d −1), or: mol·m −2 ·d −1.
is the classical electron radius (~2.82 fm, is about 7.94 × 10 −30 m 2 or 79.4 mb) / ′ is the ratio of the wavelengths of the incident and scattered photons; is the scattering angle (0 for an undeflected photon).
Radiation pressure can be viewed as a consequence of the conservation of momentum given the momentum attributed to electromagnetic radiation. That momentum can be equally well calculated on the basis of electromagnetic theory or from the combined momenta of a stream of photons, giving identical results as is shown below.
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