Dynamic interference in the 2+1 photon resonance-enhanced multiphoton ionization of Li

Multiphoton excitation and subsequent ionization of atomic systems is a widely studied

area. Under the influence of a strong resonant laser field the electronic states are subject

to a time-dependent coupling and repel each other. If the pulse supports many optical cycles,

this ac Stark shift of the energy levels follows the pulse envelope. Accordingly, electrons

emitted in the rising and falling edge of the pulse will have the same energy, but their

time delay will give rise to an interference pattern in the spectra. In our earlier work [1]

we investigated the two-photon Rabi oscillations induced between the 2s and 4s states of

the Li atom and probed the dynamics with the photoelectron spectra obtained by the

absorption of a third photon from the same pulse. Employing a three-state model we

highlighted the connection between the dynamic interference structures of the spectra

and the Stark shifts and two-photon Rabi frequency. The present work is our attempt to

validate the predictions of the three-state model with ab-initio calculations in the

single-active-electron picture [2].

[1] A. Tóth, A. Csehi, J. Phys. B 54 (2021) 035005

[2] A. Tóth, A. Csehi, Phys. Rev. A 104 (2021) 063102