Laser–microwave methods for precise determination of the fine and hyperfine structure of Li⁺ ions

Three methods were developed for the determination of the fine and hyperfine structures of helium-like Li⁺ ions in a metastable state 1s2s³S₁ and in a short-lived multiplet 1s2p³P: hyperfine structure (hfs) spectroscopy of the 2 ³S₁ state using laser optical pumping and microwave transition; hfs investigation of the 2 ³P multiplet by laser excitation and microwave-induced optical pumping of the 2 ³S₁ state; rf controlled spectroscopy of large term splitting with the aid of two dye lasers. The first method was used to study the hfs splitting of the 2 ³S₁ state of the ^6,7Li⁺ isotope and the magnetic hfs interaction constants were obtained. The hfs anomaly was in good agreement with the results obtained from the hfs splitting of the ground state of the atom. A small shift of the 2 ³S₁, F = 3/2 level of the ⁷Li⁺ ion, which was due to the hyperfine shift of the ¹S and ³S levels, was measured. This was done using the second method and microwave measurements were made also of the 2 ³P state ⁷Li⁺.