Magnetic field--induced modification of selection rules for Rb D${}_2$ line monitored by selective reflection from a vapor nanocell

Magnetic field-induced giant modification of the probabilities of five transitions of $5S_{1\mathrm{/}2},F_g=2\to 5P_{3\mathrm{/}2},F_e=4$ of ${}^{85}$Rb and three transitions of $5S_{1\mathrm{/}2},F_g=1\to 5P_{3\mathrm{/}2},F_e=3$ of ${}^{87}$Rb forbidden by selection rules for zero magnetic field has been observed experimentally and described theoretically for the first time. For the case of excitation with circularly-polarized (${\sigma }^{+}$) laser radiation, the probability of $F_g=2,m_F=-2\to F_e=4,m_F=-1$ transition becomes the largest among the seventeen transitions of ${}^{85}$Rb $F_g=2 \rightarrow F_e=1,2,3,4$group,andtheprobabilityof$F_g=1,~m_F=-1 \rightarrow F_e=3,~m_F=0$transitionbecomesthelargestamongtheninetransitionsof$^{87}$Rb$F_g=1 \rightarrow F_e=0,1,2,3$ group, in a wide range of magnetic field 200 – 1000 G. Complete frequency separation of individual Zeeman components was obtained by implementation of derivative selective reflection technique with a 300 nm-thick nanocell filled with Rb, allowing formation of narrow optical resonances. Possible applications are addressed. The theoretical model is perfectly consistent with the experimental results.