Observation of the Magneto-Optic Voigt Effect in a Paramagnetic Diamond Membrane

TL;DR

This paper reports the first observation of the magneto-optic Voigt effect in a synthetic diamond membrane with nitrogen defects, demonstrating quadratic magnetic field dependence and laser-modifiable polarization rotation, with implications for quantum sensing.

Contribution

It presents the experimental observation of the Voigt effect in a diamond membrane with nitrogen defects, including the effects of laser illumination on magnetisation and spectral properties.

Findings

Polarisation rotation is quadratically proportional to magnetic field and reflection angle.

Laser illumination modulates the magnetisation and spectral distribution.

Spectral narrowing indicates a small increase in magnetisation without heating degradation.

Abstract

The magneto-optic Voigt effect is observed in a synthetic diamond membrane with a substitutional nitrogen defect concentration in the order of 200 ppm and a nitrogen-vacancy defect sub-ensemble generated through neutron irradiation and annealing. The measured polarisation rotation in the reflected light is observed to be quadratically proportional to the applied magnetic field and to the incident reflection angle. Additionally, it is observed to be modifiable by illuminating the diamond with a 532 nm laser. Spectral analysis of the reflected light under 532 nm illumination shows a slow narrowing of the spectral distribution, indicating a small increase in the overall magnetisation, as opposed to magnetisation degradation caused by heating. Further analysis of the optical power dependence suggest this may be related to a shift in the spin ensembles charge state equilibrium and, by extension, the resulting ensemble magnetisation.