Xufei Sun

Revealing backward rescattering photoelectron interference of molecules in strong infrared laser fields

Photoelectrons ionized from atoms and molecules in a strong laser field are either emitted directly or rescattered by the nucleus, both of which can serve as efficiently useful tools for molecular orbital imaging. We measure the photoelectron angular distributions of molecules (N2, O2 and CO2) ionized by infrared laser pulses (1320u2005nm, 0.2 ~ 1 × 1014u2005W/cm2) from multiphoton to tunneling regime and observe an enhancement of interference stripes in the tunneling regime. Using a semiclassical rescattering model with implementing the interference effect, we show that the enhancement arises from the sub-laser-cycle holographic interference of the contributions of the back-rescattering and the non-rescattering electron trajectory. It is shown that the low-energy backscattering photoelectron interference patterns have encoded the structural information of the molecular initial orbitals and attosecond time-resolved dynamics of photoelectron, opening new paths in high-resolution imaging of sub-Ångström and sub-femtosecond structural dynamics in molecules.

Tunnelling coordinates of high-energy photoelectrons in above-threshold ionization

With a three-dimensional semiclassical ensemble simulation, we comprehensively analyse the underlying dynamics of the photoelectron energy plateau (with an energy ranging from 2Up to 10Up, Up is the ponderomotive energy) from the single ionization of atoms in strong linearly polarized laser fields. We study the initial tunnelling coordinates at the tunnel exit (tunnelling phase and initial transverse momentum) of those high-energy photoelectrons. The rescattering process is very sensitive to the initial transverse momentum at the tunnel exit. We further identify the significant role of the long-range Coulomb potential on the rescattering process, which is usually ignored for those high-energy plateau electrons. Depending on the initial tunnelling coordinates, multiple forward scattering plus a hard collision has a significant contribution to the yield of the high-energy photoelectrons. By analysing the tunnelling coordinates of rescattering electrons, this provides sophisticated information for other related rescattering processes, i.e., high-harmonic generation and nonsequential double ionization.