One and two-center processes in high-order harmonic generation in diatomic molecules: influence of the internuclear separation

TL;DR

This paper investigates how one- and two-center recombination processes affect high-order harmonic generation in diatomic molecules, revealing interference patterns and the impact of internuclear separation using a modified strong-field approximation.

Contribution

It introduces a modified saddle-point approach that incorporates molecular structure to analyze interference effects in HHG from diatomic molecules.

Findings

Two-center interference patterns arise from quantum interference of different orbital trajectories.

Contributions from different centers vary in magnitude due to potential-energy shifts.

Similar interference effects can be modeled with single-atom saddle-point equations with appropriate molecular factors.

Abstract

We analyze the influence of different recombination scenarios, involving one or two centers, on high-order harmonic generation (HHG) in diatomic molecules, for different values of the internuclear separation. We work within the strong-field approximation, and employ modified saddle-point equations, in which the structure of the molecule is incorporated. We find that the two-center interference patterns, attributed to high-order harmonic emission at spatially separated centers, are formed by the quantum interference of the orbits starting at a center $C_{j}$ and finishing at a different center $C_{\nu }$ in the molecule with those starting and ending at a same center $C_{j}.$ Within our framework, we also show that contributions starting at different centers exhibit different orders of magnitude, due to the influence of additional potential-energy shifts. This holds even for small internuclear distances. Similar results can also be obtained by considering single-atom saddle-point equations and an adequate choice of molecular prefactors.