Above threshold ionisation - Multiphoton ionization involving continuum-continuum transitions

Pierre Agostini, G. Petite

Piers Coleman, P. L. Knight, Keith R. Burnett

H. B. van Linden van den Heuvell, Harm Geert Muller, Marnix J. van der Wiel

Alexandr V. Belousov, V.A. Kovarsky, O. B. Prepelitsa

Maciej Lewenstein, Jan Mostowski, Marek Trippenbach

The authors derive equations describing non-resonant multiphoton ionisation of atoms in strong laser fields. The equations lead to a multichannel decay of the bound state as well as continuum-continuum (CC) relaxation.

R. Parzyński

Two-laser multiphoton ionisation under the autoionising-like resonance condition is studied theoretically within an extended atomic model dictated by the experiment of Feldmann et al (1986). Ordinary coupling between a selected pair of bound states via the continuum only is supplemented in the author's model by Raman-type coupling involving the atomic spectrum below the ionisation threshold. In the case considered this additional Raman coupling enhances the ionisation rate to a much greater extent than the coupling via the continuum can do. The Raman coupling modifies the autoionising-like shape parameter and is decisive as far as the resonance peak profile is concerned. Exploiting this Raman coupling within the atomic model with four effective bound states, the author gives explanations for all the details of the ionisation spectrum detected by Feldmann et al, i.e. the number of resonance peaks, their strength, fine structure, shape, relative heights and sensitivity to the laser field.