Control of the helicity of high-order harmonics generated by bicircular field

TL;DR

This paper theoretically explores how to generate circularly polarized high-harmonic pulses with helicity asymmetry using bicircular laser fields, analyzing different atomic systems and field configurations to optimize harmonic intensity and helicity control.

Contribution

It demonstrates how to achieve helicity asymmetry in high-order harmonics by tuning bicircular field intensities, especially for He and Ne atoms, advancing circular polarization control in high-harmonic generation.

Findings

Helicity asymmetry can be maximized with specific bicircular field configurations.

He atoms produce strong positive helicity harmonics with ω--3ω fields.

Ne atoms exhibit large helicity asymmetry over a wider parameter range.

Abstract

High-order harmonics generated by bicircular laser field have helicities which alternate between $+1$ and $-1$. In order to generate circularly polarized high-harmonic pulses, which are important for applications, it is necessary to achieve asymmetry in emission of harmonics having opposite helicities. We theoretically investigated a wide range of bicircular field component intensities and found areas where both the harmonic intensity is high and the helicity asymmetry is large. We investigated the cases of $\omega$--$2\omega$ and $\omega$--$3\omega$ bicircular fields and atoms having the $s$ and $p$ ground states, exemplified by He and Ne atoms, respectively. We have shown that for He atoms strong high harmonics having positive helicity can be generated using $\omega$--$3\omega$ bicircular field with a much stronger second field component. For Ne atoms the helicity asymmetry can be large in a wider range of the driving field component intensities and for higher harmonic orders. For the stronger second field component the harmonic intensity is higher and the helicity asymmetry parameter is larger for higher harmonic orders. The results for Ne atoms are illustrated with the parametric plots of elliptically polarized attosecond high-harmonic field.