 Sum-frequency generation

A nonlinear optics process producing a field at the sum of two input angular frequencies. The driven electric polarization contains a term proportional to the product of the input complex amplitudes. With undepleted plane-wave inputs, integration along a crystal gives an output amplitude proportional to $L{e}^{i\Delta kL/2}\mathrm{sinc}(\Delta kL/2)$; the sinc function therefore determines the ideal length and phase mismatch dependence. A nonzero initial output field also interferes with this generated field.

Sum-frequency generation (SFG) is a nonlinear optical process in which two photons with different frequencies interact within a nonlinear medium to produce a new photon with a frequency that is the sum of the two original frequencies. This process is based on the principle of nonlinear optics, where the polarization of a medium becomes dependent on the intensity of the electric field.