We present a theoretical study of the optical-radio-frequency (rf ) double resonance on hyperfine ground states of alkali-metal atoms in the geophysical magnetic-field range, in which resonance circularly polarized laser light is used in the optical pumping and detection processes. The analytical expressions of the rf resonance signals corresponding to two ground states are obtained based on atomic multipole moments, where the alignment effect is considered and that is responsible for the resonance shape and linewidth especially when the optical power is relatively strong. In addition, we also obtain the analytical expressions of the linewidths of two separated resonance peaks and one presenting the competition process of the optical pumping, rf field and spin-exchange collision. Two different types of light narrowing phenomena are investigated by comparing the longitudinal relaxation rates of atomic multipole moments for two ground states. Applied to rubidium and cesium atoms, we show a particularly close agreement of our analytical results with more elaborate calculations using density-matrix theory. Our theoretical model is relevant for optimizing the sensitivity of magnetometers.

We theoretically and experimentally investigate the laser-detected magnetic resonance spectra dressed by a radio-frequency magnetic field in F g  = 4 of D1 line of cesium atoms. The analytical expression of the transmission spectrum for magnetic resonance dressed by a radio-frequency magnetic field is derived and has substantial agreement with the transmission spectra observed in the experiment. The theoretical prediction of the ratio of the amplitudes of the two sidebands with the detuning is basically consistent with the experimental data, which confirms the validity of the analytical expression. The separation between the two sidebands under resonance shows a highly linear proportion to the amplitude of the dressing field, which may provide a useful scheme for the measurement of radio-frequency magnetic field and magnetic imaging.

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