Three-colour four-photon resonant excitation of the even-parity autoionizing resonances in Yb I

We report new data on the even-parity autoionizing resonances due to the 4f inner-shell excitation in ytterbium using a three-colour four-photon resonant excitation technique. The spectra were observed using three dye lasers simultaneously pumped by a common Nd:YAG laser in conjunction with a thermionic diode ion detector. More than 50 new levels corresponding to the 4f136s2nl Rydberg series have been detected. The data were analysed in the light of the spectral lineshapes, parent ion configurations and quantum defect approach. (author)