Splitting of the electromagnetically induced transparency resonance on $^{85}$Rb atoms in strong magnetic fields up to the Paschen–Back regime

Electromagnetically induced transparency (EIT) resonance in strong magnetic fields of up to $1.7$ kG has been investigated with the use of a 30-$\mu$m cell filled with an atomic rubidium vapor and neon as a buffer gas. The EIT resonance in the $\Lambda$ system of the D1 line of 85Rb atoms has been formed with the use of two narrowband ($Ў­1$ MHz) $795$-nm diode lasers. The EIT resonance in a longitudinal magnetic field is split into five components. It has been demonstrated that the frequencies of the five EIT components are either blue- or red-shifted with an increase in the magnetic field, depending on the frequency $\nu _P$ of the probe laser. In has been shown that in both cases the $^{85}$Rb atoms enter the hyperfine Paschen-Back regime in magnetic fields of $>1$ kG. The hyperfine Paschen-Back regime is manifested by the frequency slopes of all five EIT components asymptotically approaching the same fixed value. The experiment agrees well with the theory.