Better magneto-optical filters with cascaded vapor cells

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, to the best of our knowledge, 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.