Self-consistent extraction of photoabsorption time delays in attosecond streak camera

Abstract

Photoionization can generally be decomposed into a photoabsorption process plus a half-scattering process. The streaking time delay observed in the attosecond streak camera, correspondingly, can be decomposed into a photoabsorption time delay and a continuum time delay. We propose a self-consistent method to account for the potential-laser coupling effect and extract the intrinsic absorption time delay, without invoking an implicit assumption of a constant continuum correction made in previous streaking studies. The concept is based on an iterative technique starting from an initial guess of the absorption time delay and using classical electron trajectories to consistently remove the coupling-induced momentum shift to the streak signal. We show that the self-consistent iterative algorithm converges quickly and is robust against different initial guesses. The method is applied to laser-induced ionization of atoms to obtain the absorption time delay in resonant two-photon ionization and to explore possible time delays in above-threshold ionization. The results confirm an absorption time delay linearly dependent on the ionizing pulse duration in resonant two-photon ionization. The method is also shown to perform better than conventional methods and to identify a small negative absorption time delay (less than 2 attoseconds) in above-threshold ionization.