ATOMIC IONIZATION BY AN INTENSE LASER PULSE: THE CONTINUUM-CONTINUUM COUPLING

M. G. BUSTAMANTE; V. D. RODRÍGUEZ

Foz do Iguaçu

Workshop; 19th INTERNATIONAL LASER PHYSICS WORKSHOP; 2010

University of Sao Paulo, Brazil

In this work we introduce a model accounting for full initial state coupling to the continuum plus further continuum-continuum transitions. The model also considers transitions between initial state and other discrete states. Further discrete-discrete or discrete-continuum transitions are neglected. The calculations are made in the velocity gauge. The present model leads to a single integro-differential equation for the initial state amplitude which is easily solved using the Goldfine prescription1. We have demonstrated analytically, that the sum of all transition probabilities is unity,  i.e., the model is unitary.       As a test for the model, we show in figure (a), the survival probabilities of Hydrogen under a 20 cycles XUV laser pulse (ω=0.6 a.u.). A laser field amplitude E0=0.2 a.u. (1.4×1015 W/cm2) is considered.  We also show full time dependent Schrödinger equation simulations (TDSE) performed with the Qprop2.  The comparison is rather good for the entire time interval.  In the same figure the calculations without the continuum-continuum coupling are displayed. This later results run close with full calculations and agree with TDSE results. Total ionization probabilities calculated with both models are presented. Again, the probabilities can not be distinguished in both cases. In figure (b) the ionization spectra are shown calculated with TDSE and the mentioned models. In this case, the full theory provides a much better position and height description of the principal peaks. Without continuum-continuum coupling, only odd peaks are shown. Moreover, a better account for the observed secondary structures is obtained when the theory includes the continuum-continuum coupling.