Features of alkali D2 line magnetically-induced transitions excited under π-polarized laser radiation

The impact of the optical field polarization on the spectrum of magnetically-induced transitions, a class of transitions forbidden at zero magnetic field, is studied with a weak-probe sub-Doppler technique. The high spectral resolution of the technique combined with the simplicity in interpreting the observed spectra allows to follow the behavior of individual transitions as a function of the magnetic field amplitude. We observe only one intense transition (out of 2 F g + 1 , where F is the quantum number associated with the total angular momentum of the atom) in the case of π -polarized laser radiation (a configuration where the applied magnetic field is parallel to the electric field from the laser radiation) in the F g → F g + 2 manifolds of 85 Rb, 87 Rb and 133 Cs for fields above a few hundreds of gauss. We show that this behavior is in agreement with a model based on the diagonalization of the Zeeman Hamiltonian matrix. With the rapid development of micro-machined vapor-cell-based sensors, these results will be of use to magnetometers operating above Earth field, wide-range laser frequency stabilization systems and atomic Faraday filters. • Magnetically-induced transitions of Rb and Cs D2 lines are studied with π -polarization. • An anomalous behavior of magnetically-induced transition intensities is observed. • These features are studied with a high spectral resolution technique based on nanocell. • Observed features, well described by theory, are expected for all other alkali transitions.