Observation of a laser-induced structure in the ionization continuum of sodium atoms using photoelectron energy spectroscopy

We report an experimental analysis of a structure induced by a Nd:YAG laser embedding the sodium 5S1/2 excited state in the ionization continuum. The induced structure is probed from the ground state via a one-photon ionization. The experiment is performed on an atomic beam apparatus which uses a time-of-flight spectrometer for energy analysing the emitted photoelectrons. The selectivity of this technique provides the best measurement of a laser-induced resonance in the photoionization spectrum reported to date. A good agreement is found between the theory and experimental results.