The process by which two photons with frequencies \(\nu _{2}\) and \(\nu _{3}\) combine in a non-linear medium to produce a higher energy photon with frequency \(\nu _{1}\) such that \(\nu _{1}=\nu _{2}+\nu _{3}\).
  1. Also known as a parametric upconversion or sum frequency generation. Upconversion is the reverse process of @[email protected]
  2. The efficiency of the conversion process depends on the parametric gain in the non-linear material. This in turn depends on the @[email protected] of the incident radiation, the photon frequencies, their indices of refraction in the material, and the non-linear 'hyper-susceptibility' of the material.
PAC, 2007, 79, 293. (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 437 [Terms] [Paper]