Editing Optical parametric amplifier (section)

==Optical parametric generation (OPG)==
{{main|Spontaneous parametric down conversion}}
Optical parametric generation (OPG) (also called "optical parametric fluorescence", or "[[spontaneous parametric down conversion]]") often precedes optical parametric amplification.

In [[optical parametric generation]], the input is one light beam of frequency ω<sub>p</sub>, and the output is two light beams of lower frequencies ω<sub>s</sub> and ω<sub>i</sub>, with the requirement ω<sub>p</sub>=ω<sub>s</sub>+ω<sub>i</sub>. These two lower-frequency beams are called the "signal" and "idler", respectively.

This [[light emission]] is based on the [[nonlinear optics|nonlinear optical principle]]. The [[photon]] of an incident laser pulse (pump) is, by a nonlinear optical crystal, divided into two lower-energy photons. The wavelengths of the signal and the idler are determined by the phase matching condition, which is changed, e.g. by temperature or, in bulk optics, by the angle between the incident pump laser ray and the optical axes of the crystal. The wavelengths of the signal and the idler photons can, therefore, be tuned by changing the [[phase matching]] condition.