Production of @C01130@ of frequency \(k\ \nu \)(\(k=2,3,...\)) from @C01130@ of frequency. In general, this effect is obtained through the interaction of @L03459@ light with a suitable optical medium with non-linear @P04711@. The case \(k=2\) is referred to as @F02527@, \(k=3\) is frequency tripling and \(k=4\) is frequency quadrupling. Even higher integer values of \(k\) are possible.