Above-threshold ionization spectra asymmetrically broadened in the extreme-ultraviolet pulse train and infrared laser fields

Abstract

We experimentally investigate the atomic ionization process in an extreme-ultraviolet (XUV) pulse train generated by the high-order harmonic generation process and an IR laser field. Compared with the electron spectrum ionized only by the XUV pulse train, the electron energy spectra generated in the two-color field exhibit two characterizations: (1) the spectrum is smoothed in the presence of a weak IR field, and (2) the spectrum is asymmetrically broadened when using an intense IR field. Simulation results based on the frequency-domain theory qualitatively agree with the experimental spectra. We demonstrate that the asymmetrically broadened spectrum could be interpreted by a clear two-step ionization picture: an electron wavepacket is ionized from the atomic ground state by the XUV pulse train, and then the energy of it is asymmetrically changed by absorbing or emitting specific IR photons.

Angle-resolved photoelectron energy spectrum from the high-order above-threshold ionization process in IR+XUV two-color laser fields

“…Also, these sidebands have been applied in investigating the molecular orbitals of O 2 , H 2 O and N 2 [40]. Additionally, the ATI spectrum presents a steplike structure when the XUV photon energy is much higher than the atomic ionization potential [41,42] and the dependence of ATI spectrum on polarization direction of two-color laser fields is identified [43]. Recently, the ATI process of atoms and ions in vortex XUV Bessel beam in the presence of a strong IR laser field was investigated [44].…”