Double ionization

Double ionization is a process of formation of doubly charged ions when laser radiation or charged particles like electrons[1], positrons[2] or heavy ions[3] are exerted on neutral atoms or molecules.

[4] Non-sequential double ionization is a process whose mechanism differs (in any detail) from the sequential one.

The phenomenon of non-sequential double ionization was experimentally discovered by Suran and Zapesochny for alkaline earth atoms as early as 1975.

[5] Despite extensive studies, the details of double ionization in alkaline earth atoms remain unknown.

[6] [7] [8] [9] [10] [11] For noble gas atoms, non-sequential double ionization was first observed by L'Huillier.

[12][13] The interest to this phenomenon grew rapidly after it was rediscovered[14][15] in infrared fields and for higher intensities.

For noble gas atoms in infrared laser fields, following one-electron ionization, the liberated electron can recollide with the parent ion.

[18][19] This electron acts as an "atomic antenna",[19] absorbing the energy from the laser field between ionization and recollision and depositing it into the parent ion.

Inelastic scattering on the parent ion results in further collisional excitation and/or ionization.

Dynamics of double ionization within the three-step model strongly depends on the laser field intensity.

The maximum energy (in atomic units) gained by the recolliding electron from the laser field is

Second, the time delay between the ejection of the first and the second electron is of the order of the quarter-cycle of the driving field.

If after the recollision, the electrons are ejected with a substantial delay (quarter-cycle or more), they end up going in the opposite directions.

These two types of dynamics produce distinctly different correlated spectra (compare experimental results [16][17][20][21][22] with .