Shifting nodal-plane suppressions in high-order harmonic spectra from diatomic molecules in orthogonally polarized driving fields

TL;DR

This paper investigates how nodal planes in diatomic molecules affect high-order harmonic spectra under orthogonal laser fields, revealing distortions that help map electron return angles and comparing different computational forms.

Contribution

It introduces a semi-analytical approach to analyze nodal plane effects in high-harmonic spectra, highlighting the advantages of the velocity form and the impact of elliptically polarized fields.

Findings

Nodal plane suppression distortions can be used to map electron return angles.

Velocity form of the dipole operator provides better information than length form.

Elliptically polarized fields cause larger spectral distortions.

Abstract

We analyze the imprint of nodal planes in high-order harmonic spectra from aligned diatomic molecules in intense laser fields whose components exhibit orthogonal polarizations. We show that the typical suppression in the spectra associated to nodal planes is distorted, and that this distortion can be employed to map the electron's angle of return to its parent ion. This investigation is performed semi-analytically at the single-molecule response and single-active orbital level, using the strong-field approximation and the steepest descent method. We show that the velocity form of the dipole operator is superior to the length form in providing information about this distortion. However, both forms introduce artifacts that are absent in the actual momentum-space wavefunction. Furthermore, elliptically polarized fields lead to larger distortions in comparison to two-color orthogonally polarized fields. These features are investigated in detail for $\mathrm{O}_2$, whose highest occupied molecular orbital provides two orthogonal nodal planes.