Solid-like high harmonic generation from rotationally periodic systems

TL;DR

This paper introduces a theoretical model for high harmonic generation in rotationally periodic systems, demonstrating solid-like HHG behavior in a ring-shaped molecule, and establishing a link between gas and solid HHG phenomena.

Contribution

It develops a quasi-band model for rotationally invariant systems and reveals solid-like HHG features in a cyclo[18]carbon ring, expanding understanding of HHG beyond translational symmetry.

Findings

Explicit selection rules for circular polarization harmonics.

Solid-like HHG observed in linearly polarized fields.

Potential for optical detection of molecular symmetry.

Abstract

High harmonic generation (HHG) from crystals in strong laser fields has been understood by the band theory of solid, which is based on the periodic boundary condition (PBC) of translational invariant. For systems having PBC of rotational invariant, in principles an analogous Bloch theorem can be developed and applied. Taking a ring-type cluster of cyclo[18]carbon as a representative, we theoretically suggest a quasi-band model and study its HHG by solving time-dependent Liouville-von Neumann equation. Under the irradiation of circularly polarized laser, explicit selection rules for left-handed and right-handed harmonics are observed, while in linearly polarized laser field, cyclo[18]carbon exhibits solid-like HHG originated from intra-band oscillations and inter-band transitions, which in turn is promising to optically detect the symmetry and geometry of controversial structures. In a sense, this work presents a connection linking the high harmonics of gases and solids.