Lithium Faraday filter: some like it hot

Magnetically induced rotation of linearly polarized light near an atomic resonance, combined with Doppler-broadened absorption windows, enables narrowband transmission of optical frequencies. A narrowband (2.2 GHz) lithium vapor Faraday filter at about 671 nm is investigated experimentally and theoretically. The resulting Faraday filter transmittance is demonstrated using a lithium heat pipe oven under longitudinal magnetic fields ranging from 0 to 300 G. The optimized lithium Faraday filter exhibits the peak transmittance of 82% with commonly chosen optimal parameters around the ⁷Li transitions center. The lithium <i>D₁</i>- and <i>D₂</i>-transitions are only 10 GHz apart, and temperature broadening leads to an overlap of the isotopes' <i>D</i>-lines. Thus, the applied theoretical model needs to consider both transitions simultaneously. For this purpose, we extended an existing Python library (ElecSus), which now allows for the calculation of the atomic susceptibilities of lithium.