Nonlocal current-response theory of structured-light dichroism

TL;DR

This paper presents a microscopic, nonlocal response theory for optical absorption and structured-light dichroism, revealing how light-matter interactions depend on mode structure, symmetry, and nonlocal effects.

Contribution

It introduces a comprehensive nonlocal minimal-coupling framework that describes structured-light dichroism and mode-resolved responses in optical systems.

Findings

Derived a general expression for light absorption as a bilinear functional of the electromagnetic potential.

Identified dichroic signals as helicity-odd projections of the nonlocal response kernel.

Resolved the response into symmetry, tensorial, and mode-space sectors, revealing mode-specific selection rules.

Abstract

We develop a microscopic theory of optical absorption and structured-light dichroism in a nonlocal minimal-coupling framework. Starting from the minimal-coupling Hamiltonian, we express absorption as a bilinear functional of the electromagnetic vector potential and the nonlocal current response, providing a general description of light--matter coupling in optical vortex beams and other inhomogeneous fields. Dichroic signals are identified as helicity-odd projections of the nonlocal response kernel, and the response is resolved into symmetry, tensorial, and mode-space sectors. For single helical modes, the theory yields diagonal OAM-resolved contributions together with the corresponding selection rules and symmetry constraints. For mixed modes, interference between distinct OAM components provides access to off-diagonal coherence of the nonlocal kernel, with a tensor structure determined by the polarization composition of the field. The theory also clarifies how local structures associated with symmetric spatial dispersion, optical chirality, and tensorial anisotropy emerge as gradient-level manifestations of the underlying nonlocal response.