multiphoton ionization

in mass spectrometry
Occurs when an atom or molecule and their concomitant ions have energy states whereby the energy in two or more photons is absorbed.
PAC, 1991, 63, 1541. 'Recommendations for nomenclature and symbolism for mass spectroscopy (including an appendix of terms used in vacuum technology). (Recommendations 1991)' on page 1548 (