Two-center minima in harmonic spectra from aligned polar molecules

TL;DR

This paper extends a two-center interference model to include superpositions of opposite orientations in aligned polar molecules, revealing how interference minima depend on recombination strength and Stark effects.

Contribution

It introduces a new model accounting for opposite orientation superpositions and Stark effects, explaining interference minima shifts in harmonic spectra of polar molecules.

Findings

Interference minima depend on recombination strength, not just phase.

Superposition of opposite orientations explains minima in aligned CO.

Stark effect causes a shift in the interference minimum due to an extra phase.

Abstract

We extend a model of two-center interference to include the superposition of opposite orientations in aligned polar molecules. We show that the position of the minimum in the harmonic spectrum from both aligned and oriented CO depends strongly on the relative recombination strength at different atoms, not just the relative phase. We reinterpret the minimum in aligned CO as an interference between opposite orientations, and obtain good agreement with numerical calculations. Inclusion of the first-order Stark effect shifts the position of the interference minimum in aligned CO even though aligned molecules do not posses total permanent dipoles. We explain the shift in terms of an extra phase that the continuum electron of oriented CO accumulates due to the Stark effect.