Spin-noise spectroscopy of optical light shifts

Light-induced nonequilibrium spin-noise spectroscopy is theoretically and experimentally shown to be an efficient technique to reveal the structure and coherent effects in a probed transition. Indeed, using metastable helium, the spin-noise spectrum is shown to exhibit a dual-peak structure around the Larmor frequency. This feature is due to the light shifts of the involved levels and strongly depends on the probe power, detuning, and polarization orientation. Both numerical and analytical models reproduce very well the details of the split spin-noise spectra: This technique thus allows a simple and direct measurement of the light shifts, and its polarization dependence permits to reveal the level structure in a nonambiguous manner.