High-order harmonic generation in polyatomic molecules induced by a bicircular laser field

TL;DR

This paper explores high-order harmonic generation in polyatomic molecules using bicircular laser fields, revealing how molecular symmetry influences harmonic emission patterns and helicity asymmetries.

Contribution

It demonstrates the role of bicircular fields in probing molecular symmetry and shows how emission asymmetries depend on molecular orientation.

Findings

Harmonics follow specific selection rules based on molecular symmetry.

BF₃ exhibits helicity asymmetry similar to atomic p states.

Harmonic emission depends on molecular orientation.

Abstract

High-order harmonic generation by a bicircular field, which consists of two coplanar counter-rotating circularly polarized fields of frequency $r\omega$ and $s\omega$ ($r$ and $s$ are integers), is investigated for a polyatomic molecule. This field possesses dynamical symmetry, which can be adjusted to the symmetry of the molecular Hamiltonian and used to investigate the molecular symmetry. For polyatomic molecules having the $C_{r+s}$ symmetry only the harmonics $n=q(r+s)\pm r$, $q=1,2,\ldots$, are emitted having the ellipticity $\varepsilon_n=\pm 1$. We illustrate this using the example of the planar molecules BH$_3$ and BF$_3$, which obey the $C_3$ symmetry. We show that for the BF$_3$ molecule, similarly to atoms with a $p$ ground state, there is a strong asymmetry in the emission of high harmonics with opposite helicities. This asymmetry depends on the molecular orientation.