Orbital angular momentum control of third-harmonic generation and vortex dichroism in isotropic media [Invited]

Krukowski, Szymon and Forbes, Kayn ORCID: https://orcid.org/0000-0002-8884-3496 (2026) Orbital angular momentum control of third-harmonic generation and vortex dichroism in isotropic media [Invited]. Journal of the Optical Society of America B, 43 (10). ISSN 0740-3224

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Abstract

Structured light carrying orbital angular momentum enables new regimes of nonlinear light–matter interaction. Here, we develop a molecular quantum electrodynamics description of third-harmonic generation (THG) driven by focused Laguerre–Gaussian beams in isotropic molecular media. We show that the nonparaxial longitudinal field components of a tightly focused beam permit THG with circularly polarized excitation in an isotropic fluid, a process forbidden for plane waves and paraxial beams. Within the electric-dipole approximation, the resulting emission is achiral, although for circularly polarized excitation its spatial structure depends on the relative sign of σ through nonparaxial spin–orbit coupling. Including electric–magnetic dipole interference introduces a chiral contribution to the nonlinear response, giving rise to third-harmonic vortex dichroism (THVD). The emitted intensity then acquires a component linear in the topological charge , reversing sign with either the wavefront handedness or molecular chirality. Numerical modeling reveals corresponding spatial asymmetries in the harmonic field. These results establish both an allowed pathway for circularly polarized THG in isotropic fluids and the first, to our knowledge, chiroptical analog of THG in such media, identifying orbital angular momentum as a new control parameter for nonlinear chiral spectroscopy.

Item Type:	Article
Additional Information:	Data availability: Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
Faculty \ School:	Faculty of Science > School of Chemistry, Pharmacy and Pharmacology
Depositing User:	LivePure Connector
Date Deposited:	06 Jul 2026 14:52
Last Modified:	06 Jul 2026 23:02
URI:	https://ueaeprints.uea.ac.uk/id/eprint/103668
DOI:	10.1364/JOSAB.600313

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