upconversion 

https://doi.org/10.1351/goldbook.U06574
The process by which two photons with frequencies ν2 and ν3 combine in a non-linear medium to produce a higher energy photon with frequency ν1 such that ν1=ν2+ν3.
Notes:
  1. Also known as a parametric upconversion or sum frequency generation. Upconversion is the reverse process of downconversion.
  2. The efficiency of the conversion process depends on the parametric gain in the non-linear material. This in turn depends on the power 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]
Citation: 'upconversion' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.U06574 RIS BibTex EndNote
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Last revised: February 24, 2014