MultiphotonIonisation

Multiphoton ionization is a process in atomic and molecular physics where an atom or molecule absorbs multiple photons simultaneously, leading to the ejection of an electron. This occurs when the energy of the absorbed photons exceeds the ionization potential of the atom or molecule. The probability of multiphoton ionization is highly dependent on the intensity of the incident light. At low light intensities, single-photon ionization, where one photon's energy is sufficient for ionization, is more probable. However, as the light intensity increases, the probability of absorbing multiple photons in a single event rises significantly.

This phenomenon is typically observed with high-intensity laser light, as the probability of a multiphoton event is proportional to powers of the laser intensity. For instance, a three-photon ionization process would have a probability scaling with the cube of the laser intensity. The energy of each individual photon does not need to be high enough to cause ionization on its own; rather, the sum of the energies of the absorbed photons must be greater than the binding energy of the electron. Multiphoton ionization is a fundamental process in strong-field physics and has applications in various fields, including spectroscopy, laser-induced breakdown spectroscopy, and the study of electron dynamics in atoms and molecules.