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Spinnor

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https://en.wikipedia.org/wiki/Spontaneous_parametric_down-conversion

"Spontaneous parametric down-conversion (also known as SPDC, parametric fluorescence or parametric scattering) is a nonlinear instant optical process that converts one photon of higher energy (namely, a pump photon), into a pair of photons (namely, a signal photon, and an idler photon) of lower energy, in accordance with the law of conservation of energy and law of conservation of momentum. It is an important process in quantum optics, for the generation of entangled photon pairs, and of single photons."

In the article we are told the conversion fraction can approach 1 to 4 million, that is for every 4 million incoming photons one will convert into a pair of photons.

Question, is the above fraction a non-linear function of input beam power? These effects occur in non-linear crystals so I am guessing the answer is yes, conversion fraction is a non-linear function of input beam power, the effect is only significant with an intense input beam?

Thanks.