The photoelectric effect is one of the most basic light-matter interactions, widely utilized in probing ultrafast dynamics in atoms, molecules, and condensed matter. It has been in the research limelight for over 100 years, and most of its specific aspects are well-understood. Still, the main questions about how long the photoionization procedure takes and how to observe the particular mechanisms accountable for the measured time delay are debated.
The theory of Wigner time delay, achieved seventy years ago by Eisenbud and Wigner for scattering processes, has been broadened to characterize the timing of the photoionization procedure. The Wigner time delay is distinguished as the energy-derivative of the phase change of the emitted photoelectron wave packet. This implies that photoionization time delay can be established by the phase shift.
A research team overseen by Prof. Yunquan Liu presented the “double-pointer attoclock” scheme, in which two-colour bi-circular fields were utilized to explore the stage and amplitude of radiating wave packets in atomic multiphoton ionization (2018). Lately, this research team has transferred this technique from atoms to molecules. The results of the research have been published in the Ultrafast Science.
They evaluated the orientation-dependent photoelectron angular streaking of asymmetric CO molecules in bi-circular fields. Then they formulated a semiclassical nonadiabatic molecular quantum-trajectory Monte Carlo (MO-QTMC) prototype to disentangle the orientation-dependent behavior of molecular Coulomb interaction and molecular orbital structure on photoelectron angular diffusion.