High ellipticity of harmonics from molecules in strong laser fields of small ellipticity

TL;DR

This paper investigates how high-order harmonic generation from molecules in elliptically polarized laser fields depends on molecular alignment and laser ellipticity, revealing a large ellipticity in harmonics at small laser ellipticity.

Contribution

It provides a combined numerical and analytical study showing the influence of molecular structure and electron motion on harmonic ellipticity, highlighting a new ellipticity hump phenomenon.

Findings

Large harmonic ellipticity observed at small laser ellipticity for parallel molecular alignment.

The ellipticity hump occurs around the harmonic generation threshold.

The interplay of molecular structure and electron dynamics is crucial for this effect.

Abstract

We study high-order harmonic generation (HHG) from aligned molecules in strong elliptically polarized laser fields numerically and analytically. Our simulations show that the spectra and polarization of HHG depend strongly on the molecular alignment and the laser ellipticity. In particular, for small laser ellipticity, large ellipticity of harmonics with high intensity is observed for parallel alignment, with forming a striking ellipticity hump around the threshold. We show that the interplay of the molecular structure and two-dimensional electron motion plays an important role here. This phenomenon can be used to generate bright elliptically-polarized EUV pulses.