Triple differential cross section for sequential double photoionization of atoms by ultrashort pulses

Abstract

A time-dependent approach for calculation of the triple differential cross section of sequential double photoionization of atoms by femto- and attosecond pulses is developed. The method involves the numerical solving of a system of coupled nonstationary Schr\"odinger equations which describe the inner-shell photoionization and the following Auger decay. The shape of the spectra and the angular distributions of photoelectrons are considered in the near-threshold region for the case of photoelectron--Auger electron coincidence experiments as well as for noncoincidence measurements. As examples, the cross sections for $\mathrm{Ar}(2p)$ and $\mathrm{Kr}(3d)$ sequential double photoionization are calculated and discussed. It is shown that the cross sections strongly depend on the duration of the ionizing pulse. In contrast, the asymmetry parameters, characterizing the angular distribution of photoelectrons, are practically independent of the characteristics of the pulse.