Editing Photoionization (section)

==Tunnel ionization==
When either the laser intensity is further increased or a longer wavelength is applied as compared with the regime in which multi-photon ionization takes place, a quasi-stationary approach can be used and results in the distortion of the atomic potential in such a way that only a relatively low and narrow barrier between a [[bound state]] and the continuum states remains. Then, the electron can [[Quantum tunnelling|tunnel through]] or for larger distortions even overcome this barrier. These phenomena are called [[tunnel ionization]] and [[over-the-barrier ionization]], respectively.{{citation needed|date=November 2023}}