Theoretical and experimental study of the 6S-8S two-photon absorption cross-section in cesium atoms

The probability of a two-photon absorption (TPA) process is quantified by means of the TPA cross-section. In this work the TPA cross-section for the 6S_1/2 → 8S_1/2 transition in cesium (Cs) atoms is obtained from a theoretical and experimental approach. It is calculated using second order perturbation theory including hyperfine structure and Doppler broadening for a thermal atomic vapor. The theoretical values for the TPA cross-sections of the two allowed hyperfine transitions are σ~_3,3=3.10×10^-24 cm⁴/W and σ~_4,4=3.65×10^-24 cm⁴/W. An experiment is set up to measure these cross-sections based on the quadratic dependence between the TPA transition rate and the intensity of the laser light. Values of σ~_3,3=(3.6±1.1)×10^-24 cm⁴/W and σ~_4,4=(4.6±1.1)×10^-24 cm⁴/W are obtained from the measurements. The results show an agreement between theory and experiment. To the best of our knowledge, this is the first time that these cross-sections are reported.