How anomalous is my Faraday filter?

Abstract

The Macaluso-Corbino effect describes the optical rotation of light in the spectral proximity to an atomic resonance. One use of this effect is narrowband optical filtering. So-called Faraday filters utilize the difference of the two components of the refractive indices, which are split by the Zeeman effect in a longitudinal magnetic field. This allows for a net rotation of a linearly polarized input beam within the medium. Placing it between crossed polarizers therefore only allows light near resonance to pass. Since any resonant spectrum implies anomalous dispersion on resonance, these filters are often characterized as being based on this anomalous dispersion. This Letter analyses to what extent the anomalous dispersion and the anomalous rotation are relevant for Faraday filters. Considering the sign of the anomalous rotation introduces a strict criterion if the filter is operated in the line center or in the spectral wing of an atomic resonance.