Sodium and potassium vapor Faraday filters revisited: theory and applications

Abstract

A complete theory describing the transmission of atomic vapor Faraday filters is developed. The dependence of the filter transmission on atomic density and external magnetic field strength, as well as the frequency dependence of transmission, are explained in physical terms. As examples, applications of the computed results to ongoing research to suppress sky background, thus allowing Na lidar operation under sunlit conditions, and to enable measurement of the density of mesospheric oxygen atoms are briefly discussed.

An atomic spectrum recorded with a single-molecule light source

“…By Dopplerfree spectroscopy, all levels can be conveniently resolved. For experiments with single photons, which originate from a single molecule, we implemented a sodium Faraday anomalous dispersion optical filter (FADOF) [39][40][41]. The design is based on an atomic vapor cell between two crossed polarizers.…”

Mesospheric temperatures and sodium properties measured with the ALOMAR Na lidar compared with WACCM

“…We use Faraday anomalous dispersion optical filters (FADOF). Such filters have been described by Chen et al (1996) and Harrell et al (2009), for example. In the case of sodium, a FADOF consists of a heated sodium vapour cell surrounded by a magnet, which creates an axial magnetic field.…”

The Faraday filter-based spectrometer for observing sodium nightglow and studying atomic and molecular oxygen associated with the sodium chemistry in the mesopause region

“…The theory of operation of the Faraday filters has been completely developed in Harrell et al (2009), and is only briefly summarized here. The Faraday filters utilize the Faraday rotation of light passed through a sodium vapor in an axial magnetic field between crossed polarizers.…”

“…The Faraday filter vapor cell ovens contain regions of separate temperature control for greater stability of the filter transmission, as described in Harrell et al (2009). One temperature is set for the body of the vapor cell and the other is set for the tip of the cell where the solid or liquid Na metal resides.…”