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Optical DownConverter is an example of a non-linear optical process, in which two beams of light of different frequencies ω 1 {\displaystyle \omega _{1}} and ω 2 {\displaystyle \omega _{2}} interact, creating microwave with frequency ω 3 = ω 1 − ω 2 {\displaystyle \omega _{3}=\omega _{1}-\omega _{2}}. It is a generalization of microwave. In the latter, ω 1 = ω 2 {\displaystyle \omega _{1}=\omega _{2}} , both of which can be provided by a single light source. From a quantum mechanical perspective, ODC can be seen as result of differencing two photons to produce a microwave. Since the energy of a photon is given by
E ν = ℏ ω , {\displaystyle E_{\nu }=\hbar \omega ,}
the frequency summing ω 3 = ω 1 − ω 2 {\displaystyle \omega _{3}=\omega _{1}-\omega _{2}} is simply a statement that energy is conserved.
In a common ODC application, light from a tunable infrared laser is combined with light from a fixed frequency visible laser to produce a microwave created by a wave mixing process.