ScienceModernglobalhigh confidence

Above-threshold ionization (ATI) is a multi-photon effect in which an atom is ionized by absorbing more than the minimum number of photons energetically required for ionization.

Notes on verification

Multiple independent peer-reviewed and scholarly sources (ScienceDirect, OSTI, Springer, arXiv) consistently corroborate the definition of above-threshold ionization as absorption of more photons than the minimum required for ionization. [tier=gold indep_score=1.0 clusters=4 claim_tier=notable]

Sources