Anomalous depolarization of the 5 p 2 P 3 Õ 2 \ 8 p 2 Pj 8 transitions in atomic 87 Rb

Measurements of the linear polarization degree of the 5p P3/2→8p P j8 transitions ( j851/2,3/2) in atomic Rb are reported. The radiative transitions are electric-dipole forbidden, but electric-quadrupole allowed. In addition, because of the relatively strong spin-orbit interaction in Rb, the p-p transitions can acquire a magnetic-dipole transition strength that may be a measurable fraction of the electric-quadrupole strength. The polarization measurements can generally provide a different and sensitive way to extract the relative transition strengths. We have measured the linear polarization degree of the 5p P3/2→8p P j8 transitions over a wide range of Rb density. We report here observations of a different depolarization effect, whereby the measured polarization of the 5s S1/2→5p P3/2→8p P1/2 transition increases, while that for the 5s S1/2→5p P3/2 →8p P3/2 transition decreases with increasing Rb density. The behavior is attributed to strong laser field effects associated with the 5s S1/2→5p P3/2 resonance transition.