Measurement of the hyperfine splitting of the 9 S1/2 level in Cesium by Doppler-free two-photon spectroscopy

The hyperfine splitting for the 133Cs isotope for the 6s 2S1/2 → 9s 2S1/2 transition has been measured using Doppler-free two-photon fluorescence spectroscopy in a gas cell for the first time to our knowledge. The hyperfine splitting between the two components was measured to be 8754 (1) MHz and the magnetic dipole coupling constant (A) for the excited 9s 2S1/2 level was determined to be 109.7 (3) MHz for the 133Cs isotope. The measured values are in good agreement with the earlier reported results.