Control of electronic magnetic state population via light polarization in the 5p 3/2 6p 3/2 electric quadrupole transition in atomic rubidium

Doppler-free optical double-resonance spectroscopy is used to study the excitation sequence in room-temperature rubidium atoms. This involves a electric dipole preparation step followed by the electric quadrupole excitation. A detailed experimental and theoretical study of the dependance on the excitation beams polarization from the 420 nm decay fluorescence () is presented. When a circularly polarized preparation beam is used, it produces a strongly oriented intermediate state. In this case a linear quadrupole excitation beam transfers the oriented state to the hyperfine states. For linearly polarized preparation and quadrupole excitation beams the spectra of the hyperfine lines follow a cosine squared dependence on the angle between the polarization directions. As a consequence, it is shown that the choice of polarization configuration allows direct use of the electric quadrupole transition selection rules to control the populations of the hyperfine magnetic sublevels in the absence of external fields. This is achieved by independently enhancing or suppressing either or ±2 electric quadrupole transitions.