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Using the intensity distribution together with Mandel's formula [3] which describes the probability of the number of photon counts registered by a photodetector, the statistical distribution of photons in thermal light can be obtained. Thermal light can be modeled as a collection of harmonic oscillators.
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 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 number operator. When acting on a quantum mechanical photon number state, it returns the number of photons in mode (k, μ). This also holds when the number of photons in this mode is zero, then the number operator returns zero. To show the action of the number operator on a one-photon ket, we consider
count of photons n with energy Q p = h c/λ. [nb 2] photon flux: Φ q: count per second: s −1: T −1: photons per unit time, dn/dt with n = photon number. also called photon power: photon intensity: I: count per steradian per second sr −1 ⋅s −1: T −1: dn/dω: photon radiance: L q: count per square metre per steradian per second m − ...
The number of photons that are collected by a given detector varies, and follows a Poisson distribution, depicted here for averages of 1, 4, and 10. Signal-to-Noise [ edit ]
count of photons n with energy Q p = h c/λ. [nb 2] photon flux: Φ q: count per second: s −1: T −1: photons per unit time, dn/dt with n = photon number. also called photon power: photon intensity: I: count per steradian per second sr −1 ⋅s −1: T −1: dn/dω: photon radiance: L q: count per square metre per steradian per second m − ...
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 :