Reverse dark resonance in Rb excited by a diode laser

The origin of recently discovered reverse (opposite-sign) dark resonances has been explained theoretically and verified experimentally. It is shown that the reason for these resonances is a specific optical pumping of the ground state magnetic sublevel in a transition when the ground state angular momentum is smaller than the excited state momentum. An experiment was conducted on Rb-85 atoms in a cell, when a diode laser using the ground state hyperfine level F-g = 3 simultaneously excites spectrally unresolved hyperfine levels with total angular momentum quantum numbers F-e = 2, 3 and 4. It is shown that due to differences in the transition probabilities the dominant role in total absorption and fluorescence signals is played by absorption on a transition F-g = 3 --> F-e = 4.