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 5s(1/2) -> 5p(3/2) -> 6p(3/2) excitation sequence in room-temperature rubidium atoms. This involves a 5s(1/2) -> 5p(3/2) electric dipole preparation step followed by the 5p(3/2) -> 6p(3/2) electric quadrupole excitation. A detailed experimental and theoretical study of the dependance on the excitation beams polarization from the 420 nm decay fluorescence (6p(3/2) -> 5s(1/2)) is presented. When a circularly polarized preparation beam is used, it produces a strongly oriented 5p(3/2) intermediate state. In this case a linear quadrupole excitation beam transfers the oriented state to the 6p(3/2) hyperfine states. For linearly polarized preparation and quadrupole excitation beams the spectra of the 6p(3/2) 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 6p(3/2) hyperfine magnetic sublevels in the absence of external fields. This is achieved by independently enhancing or suppressing either Delta M-F = +/- 1 or +/- 2 electric quadrupole transitions.