Theoretical Studies of Ultrafast Electron Dynamics in Atoms and Molecules via High-Order Harmonic Generation

Abstract

The interaction of atoms and molecules with strong laser pulses is of fundamental interest in physics and chemistry. Notably, the process known as high-order harmonic generation (HHG) refers to the production of extreme-ultraviolet (XUV) light, which occurs when an ensemble of atoms or molecules is subjected to a strong infrared laser field. Characterized by an attosecond time scale (1 as = 10-18 s), the HHG process provides the capability for experimental measurements to capture the ultrafast motion of electrons in these target atoms and molecules. The underlying physical mechanism behind this process naturally leaves imprints in the properties of the emitted XUV light, for instance, in the spectral amplitudes and phases. Within the single-atom or molecule description of HHG, we present theoretical and numerical studies based on (semi)classical and quantum approaches for treating the interactions with the long-range Coulomb and laser fields simultaneously in the electron dynamics. Using the classical trajectory Monte Carlo method, we examine the role of the atomic Coulomb potential in the single active electron dynamics responsible for the HHG process driven by an elliptically polarized laser field. Next, we apply quantum mechanical approaches to account for dynamical multielectron effects in molecular HHG. In particular, we numerically solve the time-dependent Schrödinger equation for a molecular model with two active electrons, each restricted to one dimension. Furthermore, we employ the time-dependent density functional theory approach to model the strong field dynamics of multiple active orbitals in more realistic full-dimensional molecular systems.