Better magneto-optical filters with cascaded vapor cells in the Faraday-Faraday and Faraday-Voigt geometries

TL;DR

This paper demonstrates improved magneto-optical filters by cascading vapor cells in Faraday-Faraday and Faraday-Voigt geometries, achieving record-high figure of merit with naturally-abundant rubidium vapor.

Contribution

It introduces a novel cascading approach with independent magnetic fields to enhance magneto-optical filter performance, including the first record of a Faraday-Voigt line center filter.

Findings

Achieved a FOM of 0.86 GHz$^{-1}$ with a Faraday-Faraday wing filter.

Recorded a FOM of 1.63 GHz$^{-1}$ for the Faraday-Voigt line center filter, the highest to date.

Experimental results agree well with theoretical predictions.

Abstract

Single-cell magneto-optical Faraday filters find great utility and are realized with either 'wing' or 'line center' spectral profiles. We show that cascading a second cell with independent axial (Faraday) or transverse (Voigt) magnetic field leads to improved performance in terms of figure of merit (FOM) and spectral profile. The first cell optically rotates the plane of polarization of light creating the high transmission window; the second cell selectively absorbs the light eliminating unwanted transmission. Using naturally-abundant Rb vapor cells, we realize a Faraday-Faraday wing filter and the first recorded Faraday-Voigt line center filter which show excellent agreement with theory. The two filters have FOM values of 0.86 and 1.63 GHz$^{-1}$ respectively, the latter of which is the largest FOM atomic line filter recorded.