Features of alkali D$_2$ 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 $2F_g+1$, where F is the quantum number associated with the total angular momentum of the atom) in the case of linear ($π$) polarization (a configuration where the applied magnetic field is parallel to the electric field from the laser radiation) in the $F_g\rightarrow F_g+2$ 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.