Measurement of the scalar third-order electric polarizability of the Cs ground state using CPT-spectroscopy in Ramsey geometry

The AC Stark shift induced by blackbody radiation is a major source of systematic uncertainty in present-day cesium microwave frequency standards. The shift is parametrized in terms of a third-order electric polarizability ${\alpha }_0^{(3)}$ that can be inferred from the static electric field displacement of the clock transition resonance. In this paper, we report on an all-optical CPT pump-probe experiment measuring the differential polarizability $\mathrm{\Delta }{\alpha }_0^{(3)}={\alpha }_0^{(3)}(F=4)-{\alpha }_0^{(3)}(F=3)$ on a thermal Cs atomic beam, from which we infer $ \alpha_0^{(3)}(F{=}4) = 2.023(6){stat}(9){syst}~Hz/(kV/cm)^2$, which corresponds to a scalar Stark shift parameter $k_s=-2.312(7{)}_{stat}(10{)}_{syst}Hz\mathrm{/}(kV\mathrm{/}cm{)}^2$. The result agrees within two standard deviations with a recent measurement in an atomic fountain, and rules out another recent result obtained in a Cs vapor cell.