Doppler-free two-photon spectroscopy of neon. II. Line intensities

Abstract

We report in this paper the principle of the calculation of the hyperfine components of a two-photon absorption line and we compare the results of the calculation with some of our expérimental results. In the first part of the paper, the two-photon transition operator is expanded on a tensorial irreductible set basis. That operator is generally the sum of two operators, one scalar and the other one quadrupolar. We deduce from it the selection rules for two-photon absorption and the formulae which permit one to calculate the intensities of the hyperfine components of a two-photon absorption line. We also report the density matrix in the excited state obtained after the two-photon excitation process, which permits one to calculate the fluorescence lines. At last we present the atomic quantities involved in the collision broadening of a two-photon absorption line. In the second part, we present the experimental hyperfine spectra obtained on the neon 21 atom for the transitions between the 3s[3/2] 2 metastable level and the 4d'[5/2] 2, 4d'[3/2] 2 and 4d[3/2] 2 excited levels. We show that the expérimental ratios between the scalar and the quadrupolar parts are very different from one transition to another. At last we compare these ratios with theoretical values obtained using the formulae of the first part. We find a good agreement between expérimental and theoretical values