https://doi.org/10.1351/goldbook.T06541
Excitation resulting from successive or simultaneous absorption of two photons by an atom or molecular entity. This term is used for successive absorption only if some of the @[email protected] of the first photon remains in the atom or molecular entity before absorption of the second photon. The simultaneous two-photon absorption can also be called @[email protected]
See:
two-photon process