Magnetic quadrupole dichroism in isotropic medium

TL;DR

This paper demonstrates that resonant excitation beyond the linear regime induces significant quadrupole dichroism in isotropic media, with potential applications in magnetometry and anisotropic bleaching studies.

Contribution

It reveals a novel quadrupole dichroism effect in isotropic media under strong resonant excitation, supported by microscopic modeling and experimental validation.

Findings

Quadrupole dichroism exhibits a 90° azimuthal dependence.

Strong resonant excitation enhances magnetic linear anisotropy.

Experimental results agree with theoretical predictions.

Abstract

For isotropic media, the magnetic field applied across the light propagation direction affects their optical properties only in the second order, and its effect proves to be much weaker than in the longitudinal field. In this work, we show that, under resonant excitation well beyond the linear regime, the situation changes drastically: A small magnetic linear anisotropy considerably increases, and an even stronger new quadrupole dichroism emerges. The latter manifests itself as the 90$^\circ$-periodic azimuthal dependence of the transmission and anisotropic rotation of the probe polarization plane. These effects are described microscopically in a toy model, and their symmetry analysis is presented. Both are observed experimentally on the D2 resonance of cesium vapor and agree with the theoretical predictions. The large magnitude of the quadrupole dichroism makes it promising for magnetometric applications and for studying the effects of anisotropic bleaching.