Two-colour three-photon excitation of 6snf F-1,3(3) and 6snp P-1(1), P-3(1,2) Rydberg levels of Yb I

We report a reinvestigation of the 6snf(1.3)F(3) (9 less than or equal to n less than or equal to 30), 6snp P-1(1) (12 less than or equal to n less th an or equal to 56), 6snp P-3(1) (12 less than or equal to n less than or eq ual to 21) and 6snp P-3(2) (12 less than or equal to n less than or equal t o 19) Rydberg states of ytterbium atom using a two-colour three-photon reso nant excitation technique through the 4f(14)6s5d D-1(2) intermediate level. The spectra were observed using two dye lasers simultaneously pumped by a common Nd:YAG laser in conjunction with a thermionic diode ion detector. So me new levels have been identified in the vicinity of the 6snf (9 less than or equal to n less than or equal to 16) Rydberg levels. Three new perturbe rs 4f(13)5d(2)6s D-3(3) at 48 584.1 cm(-1), 4f(13)5d(2)6s F-1(3) at 49 122. 4 cm(-1) and 4f(13)5d(2)6s (3)G(3) at 49 661.6 cm(-1) have been Located in addition to observation of the 6s9d D-1(2) and 6p(2) D-1(2) even parity lev els due to sequential excitation from the 6s6p P-1(1) level. The interchann el interactions among the J = 2 and J = 3 channels have been analysed using multichannel quantum defect theory.