Editing Tunnel ionization (section)

In [[physics]], '''tunnel ionization''' is a process in which [[electron]]s in an [[atom]] (or a [[molecule]]) [[Quantum tunnelling|tunnel]] through the potential barrier and escape from the atom (or molecule). In an intense [[electric field]], the potential barrier of an atom (molecule) is distorted drastically. Therefore, as the length of the barrier that electrons have to pass decreases, the electrons can escape from the atom's potential more easily.  Tunneling ionization is a [[Quantum mechanics|quantum mechanical]] phenomenon since in the classical picture an electron does not have sufficient energy to overcome the potential barrier of the atom.

When the atom is in a DC external field, the Coulomb potential barrier is lowered and the electron has an increased, non-zero probability of tunnelling through the potential barrier. In the case of an alternating electric field, the direction of the electric field reverses after the half period of the field. The ionized electron may come back to its parent ion. The electron may recombine with the [[atomic nucleus|nucleus]] (nuclei) and its kinetic energy is released as light ([[high harmonic generation]]).  If the recombination does not occur, further ionization may proceed by collision between high-energy electrons and a parent atom (molecule). This process is known as [[non-sequential ionization]].<ref>{{cite journal | last=Corkum | first=P. B. | title=Plasma perspective on strong field multiphoton ionization | journal=Physical Review Letters | publisher=American Physical Society (APS) | volume=71 | issue=13 | date=1993-09-27 | issn=0031-9007 | doi=10.1103/physrevlett.71.1994 | pages=1994–1997| pmid=10054556 | s2cid=29947935 | url=https://nrc-publications.canada.ca/eng/view/accepted/?id=c16dde3a-0d05-4437-bca6-3292fdd9d9ff }}</ref>