Above threshold ionization

In atomic, molecular, and optical physics, above threshold ionization (ATI), is a multi-photon effect where an atom is ionized with more than the energetically required number of photons. It was first observed in 1979.

In the case of ATI the photoelectron peaks should appear at

where the integer ${\displaystyle n}$ represents the minimum number of photons absorbed and the integer s represents the number of additional photons absorbed. ${\displaystyle W}$ is the ionization energy and ${\displaystyle E_{s}}$ is the electron kinetic energy of the peak corresponding to s additional photons being absorbed.

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