## upconversion

https://doi.org/10.1351/goldbook.U06574
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 $$\nu _{1}=\nu _{2}+\nu _{3}$$.
Notes:
1. Also known as a parametric upconversion or sum frequency generation. Upconversion is the reverse process of @DT07362@.
2. The efficiency of the conversion process depends on the parametric gain in the non-linear material. This in turn depends on the @P04792@ of the incident radiation, the photon frequencies, their indices of refraction in the material, and the non-linear 'hyper-susceptibility' of the material.
Source:
PAC, 2007, 79, 293. (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 437 [Terms] [Paper]