Multielectron Correlation in High-Harmonic Generation: A 2D Model Analysis

Abstract

We analyze the role of multielectron dynamics in high-harmonic generation spectroscopy, using an example of a two-electron system. We identify and systematically quantify the importance of correlation and exchange effects. One of the main sources for correlation is identified to be the polarization of the ion by the recombining continuum electron. This effect, which plays an important qualitative and quantitative role, seriously undermines the validity of the standard approaches to high-harmonic generation, which ignore the contribution of excited ionic states to the radiative recombination of the continuum electron.

Exchange and polarization effect in high-order harmonic imaging of molecular structures

“…To analyze the role of multielectron dynamics, we use the ionic eigenstate resolved (IER) expansion of the wave function [13]. First, we solve full time-dependent Schrödinger equation to find multielectron wave function.…”

“…Optimization of the multiconfiguration expansion brings the computational costs down to a level comparable with conventional one-electron calculations and opens the door to a systematic analysis of multielectron effects in HHG. For the analysis of the role of exchange and multielectron correlation effects in HHG we use an IER expansion of the multidimensional wave function [13]. This technique allows us to quantify the physical mechanisms and the role of various multielectron effects.…”

“…Radiative recombination exhibits the richness and complexity * s.sukiasyan@imperial.ac.uk of its counterpart, the one-photon ionization. Not surprisingly, harmonic emission reflects this complexity (see, e.g., [11][12][13][14]), for example, through the coupling of different recombination channels via electron-electron interaction. Channel coupling induced by the returning electron can play an important role in significantly increasing the efficiency of harmonic generation at frequencies ∼10 2 eV [14].…”

“…These include: (i) (multielectron) polarization of the bound wave function in the neutral molecule and in the ion by the laser field [13,33,34], (ii) laser-induced electronic excitations on the subcycle time scale [32,33,35,36], including excitations in the ion between ionization and recombination, (iii) correlation-induced virtual and real excitations of the ionic electrons by the returning continuum electron, immediately prior and during recombination [13,14,37], (iv) excitations of collective modes (such as plasmons) in highly polarizable molecules and clusters [38,39], by both the laser field and the recolliding electron.…”

“…However, the drawback is the need for accurate theoretical description of strong-field dynamics, starting with strong-field ionization, for both single [20][21][22][23][24][25][26][27][28] and multiple ionization channels [29][30][31]. Quantitative modeling of harmonic generation requires one to consider not only multiple ionization and recombination channels corresponding to different states of the molecular ion, but also their coupling during strong-field ionization and between ionization and recombination [13,15,32].…”