Helicity reversion in high harmonic generation driven by bichromatic counterrotating circularly polarized laser fields

TL;DR

This paper explores how high harmonic generation driven by bichromatic counterrotating circularly polarized lasers exhibits helicity reversal at specific harmonic orders, linking it to electron trajectories and classical models.

Contribution

It provides a detailed analysis of helicity reversions in high harmonics using TDSE simulations and classical trajectory models, offering new insights into polarization control in HHG.

Findings

Helicity of harmonic emission reverses at specific harmonic orders.

Reversions are linked to classical electron trajectories and ionization lobes.

Electrons ionized at different lobes produce harmonics with opposite helicities.

Abstract

We investigate the polarization properties of high harmonics generated with the bichromatic counterrotating circularly polarized (BCCP) laser fields by numerically solving time-dependent Schr\"odinger equation (TDSE). It is found that, the helicity of the elliptically polarized harmonic emission is reversed at particular harmonic orders. Based on the time-frequency analysis and the classical three-step model, the correspondence between the positions of helicity reversions and the classical trajectories of continuum electrons is established. It is shown that, the electrons ionized at one lobe of laser field can be divided into different groups based on the different lobes they recombine at, and the harmonics generated by adjacent groups have opposite helicities. Our study performs a detailed analysis of high harmonics in terms of electron trajectories and depicts a clear and intuitive physical picture of the HHG process in BCCP laser field.