Sum frequency generation

Sum-frequency generation (SFG) is an example of a second order non-linear optical process.This phenomenon is based on the annihilation of two input photons at frequencies $omega\_1$ and $omega\_2$ while, simultaneously, one photon at frequency $omega\_3$ is generated.In order that the sum-frequency generation takes place it is necessary that the following two conditions happen:

1. Energy conservation: $hbaromega\_3\; =\; hbaromega\_1\; +\; hbaromega\_2$

2. Momentum conservation: $hbar\; k\_3\; =\; hbar\; k\_1\; +\; hbar\; k\_2$

The first condition shows the relationship of the frequencies between the input and output photons. It is possible to notice that the sum-frequency generation is a generalization of second harmonic generation. In the latter, $omega\_1\; =\; omega\_2$, both of which can be provided by a single light source.The second condition implicates the k-vector conservation, in fact $Delta\; k\; =\; k\_3\; -\; k\_2\; -\; k\_1\; =\; 0$; this condition is called phase matching condition.

In a common SFG application, light from a tunable infrared laser is combined with light from a fixed infrared frequency in order to produce visible light through wave mixing process.

External links

* [http://www.advr-inc.com/waveguide.html AdvR - SFG in KTP Waveguides]