Hyperfine coupling constants of the cesium $7D_{5/2}$ state measured up to the octupole term

Abstract: We report the measurement of the hyperfine splitting in the $7D_{5/2}$ state of $^{133}$Cs using high resolution Doppler-free two-photon spectroscopy enabled by precise frequency scans using an acousto-optic modulator. All the six hyperfine levels are resolved in our spectra. We determine the hyperfine coupling constants A = -1.70867(62) MHz and B = 0.050(14) MHz which represent over 20-times improvement in the precision of both A and B. Moreover, our measurement is sufficiently precise to put bounds on the value of the magnetic octupole coupling constant C = 0.4(1.4) kHz for the $7D_{5/2}$ state. We additionally report the measurement of ac Stark shift [-46 $\pm$ 4 Hz/(W/cm$^2$)], collisional shift and pressure broadening which are important for optical frequency standards based on the $6S_{1/2} \rightarrow 7D_{5/2}$ two-photon transition.