Observing the Coulomb shifts of ionization times in high-order harmonic generation
Shengjun Yue, Jin Liu, Shan Xue, Hongchuan Du, Manfred Lein
Abstract
The Coulomb interaction between the active electron and the parent ion is inherent in high-order harmonic generation from laser-driven atoms, but it is often neglected in modeling the electron dynamics. For this reason, the pioneering measurement scheme based on orthogonally polarized two-color fields [reported in Nature (London) 485, 343 (2012)], which is able to measure ionization and return times for the electron trajectories, does not reflect the time shifts caused by the Coulomb interaction. We introduce a simple Coulomb correction to the electron motion in the two-color scheme, leading to modified retrieval equations for the extraction of time information from the observables. We apply the modified equations to data calculated from simulations of the time-dependent Schr\"odinger equation and we show that the scheme effectively reveals the Coulomb shift of the ionization time.