Inhomogeneous light shift in alkali-metal atoms

The dynamic Stark shift of an inhomogeneously broadened spectral transition has been studied. Our measurements show a shift in the observed ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$ ground-state hyperfine transition which has a nonlinear dependence on light intensity when the conditions for inhomogeneous broadening are met. The nonlinearity is the result of light-intensity gradients in the signal volume, which produce an inhomogeneously broadened asymmetric microwave transition. We show that our measurements are in full agreement with the second-order perturbation-theory treatment of light-induced energy-level shifts, when the effects of inhomogeneities are properly taken into consideration. The effects of inhomogeneous broadening must be carefully considered when extracting oscillator strengths from light-shift data, or when performing high-precision laser spectroscopy.