upconversion

https://doi.org/10.1351/goldbook.U06574
The process by which two photons with frequencies ν 2 and ν 3 combine in a non-linear medium to produce a higher energy photon with frequency ν 1 such that ν 1 = ν 2 + ν 3.
Notes:
  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.
Source:
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 437 (https://doi.org/10.1351/pac200779030293)