Investigation of lutetium Rydberg states by laser multistep resonance ionization spectroscopy

Laser multistep excitation and electric-field ionization spectroscopy have been used to investigate experimentally highly excited states (HES) of lutetium in the vicinity of the first ionization limit. The investigation includes the measurement of energy levels (ionic signal vs last transition frequency) and radiation lifetime (ionic signal vs ionizing electric-field pulse delay) of the states investigated. Even Rydberg states of 4 f ¹⁴ 6 s ² nd have been observed with two-step laser excitation. The maximum experimental error is 0.3 cm^-1 for the energy and 20% for the radiation lifetime measurements. This is the very first time that results for the lifetimes as well as for a large part of the energy values have been obtained. Our present experimental results compare well with previously calculated values obtained by relativistic perturbation theory using the zero-order model approximation, and with the available experimental values.