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High-resolution laser spectroscopy has been performed for the rare-earth elements as well as Ba by using a tunable diode laser together with a well collimated atomic beam. Hyperfine structures and isotope shifts have been measured for eight transitions in Ba I, Ce I, Sm I, Eu I, Gd I and Yb I. Hyperfine constants A and B have been determined for the 4 f 7 5 d 6 s 6 p 11 F 5 level of 155,157 Gd, and the 4 f 14 6 s 6 p 3 P 2 , 4 f 14 6 s 7 s 3 S 1 levels of 171,173 Yb. The field shifts and 6 s -electron densities at the nucleus have been derived for the studied elements and compared with the Hartree–Fock calculation.

High-resolution atomic-beam laser spectroscopy in Eu I has been performed using a tunable diode laser. The hyperfine structure (hfs) and isotope shift of the 4 f 7 6 s 2 8 S 7/2 –4 f 7 6 s 6 p 10 P 9/2 transition at 686.45 nm have been measured. The hfs constants A and B of 151 Eu and 153 Eu have been determined for the upper state 4 f 7 6 s 6 p 10 P 9/2 , and the hyperfine anomaly has been derived. The Δ F =+2 transitions, normally forbidden, have been induced by applying a magnetic field of approximately 1 G. Their intensity dependences on the magnetic field strength and on the hfs splittings agreed with the first-order perturbation theory, which considers the mixing between the closely lying hfs levels in the ground state.

High-resolution diode-laser spectroscopy has been performed on atomic beams of natural Gd and Dy. Isotope shifts of the even-mass isotopes have been measured for two transitions in Gd I and one transition in Dy I. Specific mass shifts, as well as field shifts, have been derived for transitions of 4 f 7 5 d 6 s 2 –4 f 7 6 s 2 6 p in Gd I, and 4 f 10 6 s 2 –4 f 9 5 d 6 s 2 in Dy I; the specific mass shift is much larger than the normal mass shift. It has been found that the specific mass shift of the 4 f 10 6 s 2 –4 f 9 5 d 6 s 2 transition in Dy I is about one order of magnitude larger than that of the 4 f 7 5 d 6 s 2 –4 f 7 6 s 2 6 p transition in Gd I. This shows that the specific mass shift, related to the correlation effect between electrons, strongly depends on the orbital angular momentum of electrons.

High-resolution laser spectroscopy in Sm I has been performed by using a tunable diode laser together with a highly collimated atomic beam. Hyperfine structures and isotope shifts of Sm isotopes have been measured for four transitions in the wavelength region of 636–687 nm; the largest isotope shift has been observed. Hyperfine constants A and B of 147 Sm and 149 Sm have been determined for six levels. By using the purest s 2 - s p transition with the largest isotope shift, nuclear parameters λ, changes in mean-square nuclear charge radii δ , and nuclear deformation parameters δ have been derived and discussed.