Rb vapour Zeeman optical spectroscopy in a self-calibrated magnetic field

High-resolution optical spectroscopy of Rb atoms in an intermediate-Zeeman magnetic field regime is performed. Magnetic fields between 0.05 T and 0.13 T are measured. We introduce a measurement approach based on three-level Λ Λ systems where the open-loop frequency energy separation is determined by the applied magnetic field. Using this method an accuracy better than 100 ppm is reached in a measurement series. In parallel, on the basis of complementary measurements based on three-level V systems we obtain the first experimental value of the Landé g-factor of the first excited state for ⁸⁵ 85 Rb, ⁸⁵gJ(5P1/2) 85 g J ( 5 P 1 / 2 ) =0.66709(7), and for ⁸⁷ 87 Rb, ⁸⁷gJ(5P1/2) 87 g J ( 5 P 1 / 2 ) =0.6663(2). Our approach is unprecedented in the literature for Rb. Graphic abstract Experimental results for the Land´e g-factor of the first excited state of Rb