Generalized optical theorem for propagation invariant beams

TL;DR

This paper extends the optical theorem to structured illumination sources, specifically propagation invariant beams, providing a generalized expression for electromagnetic scattering analysis.

Contribution

It derives a new optical theorem formulation for propagation invariant beams, expanding the applicability of scattering analysis beyond plane wave illumination.

Findings

Derived a generalized optical theorem for structured beams.

Analyzed scattering of Bessel beams by dielectric spheres.

Validated the theorem under Rayleigh approximation.

Abstract

Many practical applications require the analysis of electromagnetic scattering properties of local structures using different sources of illumination. The Optical Theorem (OT) is a useful result in scattering theory, relating the extinction of a structure to the scattering amplitude in the forward direction. The most common derivation of the OT is given for plane waves but advances in optical engineering now allow laser beam shaping, which might require an extended theorem where the impinging source is a structured field. In this work, we derive an expression for the optical theorem based on classical electromagnetic theory, for probe sources given in terms of propagation invariant beams. We obtain a general expression for the differential scattering cross section using the integral scattering amplitude approximation in the far field. We also analyze the scattering problem of a zero order Bessel beam by a dielectric sphere, under the Rayleigh approximation by varying the angle of incidence.