Electromagnetic theory of Helicoidal Dichroism in reflection from magnetic structures

TL;DR

This paper develops a classical electromagnetic theory explaining how reflection from magnetic structures affects light beams carrying orbital angular momentum, revealing new magnetic dichroism effects linked to symmetry and magneto-optic interactions.

Contribution

It introduces a theoretical framework for magnetic helicoidal dichroism in reflected light with OAM, including analytical formulas connecting measurable signals to MOKE constants.

Findings

Reflection alters OAM content depending on magnetization symmetry.

Three types of Magnetic Helicoidal Dichroism are identified.

MHD signals up to 10% relate to MOKE constants.

Abstract

We present the classical electromagnetic theory framework of reflection of a light beam carrying Orbital Angular Momentum (OAM) by an in-plane magnetic structure with generic symmetry. Depending on the magnetization symmetry, we find a change in the OAM content of the reflected beam due to magneto-optic interaction and an asymmetric far-field intensity profile. This leads to three types of Magnetic Helicoidal Dichroism (MHD), observed when switching the OAM of the incoming beam, the magnetization sign, or both. In cases of sufficient symmetries, we establish analytical formulas which link an experimentally accessible MHD signal up to $10\%$ to the Magneto-Optical Kerr Effect (MOKE) constants. Magnetic vortices are particularly enlightening and promising targets, for which we explore the implications of our theory in the joint publication XX XXX XXXXXX.