biphotonic excitation 

https://doi.org/10.1351/goldbook.B00668
Simultaneous (coherent) absorption of two photons (either same or different wavelength), the energy of excitation being the sum of the energies of the two photons. Also called two-photon excitation.
Note:
This term is sometimes also used for a two-step absorption.
Source:
PAC, 2007, 79, 293. (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 308 [Terms] [Paper]
Citation: 'biphotonic excitation' 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.B00668 RIS BibTex EndNote
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Last revised: February 24, 2014