Isotope ⁸⁷Rb Faraday anomalous dispersion optical filter at 420 nm.

We demonstrate a Faraday anomalous dispersion optical filter (FADOF) operating on 5S(1/2)-6P(3/2) transition at 420 nm with a 5 cm long cell of 96.5% enriched 87Rb and measure the transmission as a function of the magnetic field and temperature. The isotope 87Rb FADOF achieves a peak transmission of 98% with a bandwidth of 2.5 GHz when the temperature of the isotope 87Rb cell is 280°C and the magnetic field is 500 G. The corresponding equivalent noise bandwidth is 5.9 GHz. The isotope 87Rb FADOF is applied to submarine communications, is used as the laser frequency stabilization for some atomic lines, and is also used as the pump laser in four-level Rb active optical clock.