Nonresonant multiphoton excitation spectra of atomic 7Li

The nonresonant multiphoton laser-induced fluorescence excitation spectrum of isotopically purified 7Li was obtained with a tunable, pulsed, nanosecond laser scanned between 13 600 and 14 500 cm-1. The measured Rydberg series include n 2P -2 2S, n 2F -2 2S, n 2P -2 2P, and n 2F -2 2P, and term values up to 14 2P and 28 2F were determined. Features due to the ac Stark effect become prominent for the high Rydberg states, but can be eliminated by using circular instead of plane-polarized radiation. Quantum defect values for the n 2P, n 2D, and n 2F levels were determined. Those for the n 2F states cover a range of principal quantum numbers not previously investigated.