A modified method of Faraday rotation for investigation of atomic lines of rubidium and potassium in ultrathin cells

A nanocell filled with atomic vapors of rubidium and potassium was used to develop a modified method of Faraday rotation. The formed lines are characterized by a spectral width that is a factor of 1.5–2 smaller than those obtained by traditional method of Faraday rotation in nanocells. The new method allows obtaining the spectral width of atomic line that is 8 times smaller than the Doppler broadening in the case of the $D_2$ line of rubidium and 15 time smaller than the Doppler broadening in the case of the $D_{1,2}$ lines of potassium. In magnetic fields $B$ = 100–1200 G, all atomic lines of Rb and K atoms are spectrally resolved and identified. In the case of the $D_2$ line of Rb, it is demonstrated that the probabilities of magneto-induced transitions ($^{87}$Rb, $F_{g} = 1\to F_{e}$ = 3 and $^{85}$Rb, $F_{g}=2\to F_{e}$ = 4) can exceed the probabilities of the allowed transitions. Convenience and efficiency of the modified method of Faraday rotation for high-resolution spectroscopy is demonstrated.