Two-photon spectroscopy of some even-parity levels in neutral ytterbium

Using Doppler-free two-photon excitation from the ground state 4f¹⁴6s^{2 1}S₀ the even-parity J=2 levels of the 4f¹⁴6s7d and 4f¹⁴6s8d configurations as well as the 4f¹⁴6p², 4f¹³6s²6p and 4f¹³5d6s6p configurations between 44760.4 and 47341.8 cm^-1 in neutral ytterbium have been investigated with regard to the hyperfine structure of the excited states and the isotope shift of these transitions. The experimental results for the hyperfine splitting constants have been analysed regarding possible singlet-triplet and configuration mixing. The experimental values have been compared with theoretical results obtained in an ab initio calculation. A strong influence for the second-order hyperfine interaction could be established in both the 4f¹⁴6s7d ³D₂ and the 4f¹⁴6s10s ¹S₀ states.