PUB - Publikationen an der Universität Bielefeld

Recently, double and multiple ionizations of Kr and Xe have been observed in the field of intense femtosecond Ti : Sapphire laser pulses. Charge states upto sixfold ionization of neutral Xe atom have been measured. The observed ion yields as a function of the laser intensity violate the expectations based on the sequential mechanism by many orders of magnitude. Using a generalized "two-step-one" model of laser induced nonsequential multiple ionization of a many-electron atom, we have calculated the intensity dependence of the ion yields of Kr and Xe. Results are found to agree remarkably well with the experimental observation for all the charge states measured. They also reproduce the weak multiple knee structures seen in the experimental data. The analysis reveals the presence of nonsequential transitions involving direct escape of upto four electrons in the highest charge states considered. We conclude by predicting, for future experimental references, the intensity dependence of multiple ionization yields also from the initially prepared "target" ions of Kr and Xe, which can provide further test of the nonsequential mechanism.