Effects of coherent coupling of autoionizing states on multiphoton ionization

Abstract

Uiterwaal, Cornelis J.; Fotakis, C.; Bachau, H.; Sanchez, I.; and Cormier, E., "Effects of coherent coupling of autoionizing states on multiphoton ionization" (1996) Phys. Rev. A 53, 2587Rev. A 53, -2597Rev. A 53, (1996 [ We present the experimental and theoretical investigation of the effects of the strong electromagnetic coupling of two autoionizing states (AIS's) on the photoionization properties of an atomic system. These effects are observed by probing the ladder system from the ground state of the atom through a weak two-photon transition to the region of the lower AIS. The experimental observation of the modification of the total ionization and partial photoelectron spectra at different wavelengths of the coupling and probe lasers are accurately reproduced by a theoretical analysis which uses a density-matrix approach. Both theory and experiment indicate a strong inhibition of the ionization of the system in the case when both lasers are resonant with the two atomic transitions, while displaying a rapidly varying asymmetry induced as the detuning between the two states and the fields increases. In the extreme case of a large detuning, two separate structures appear as distinct total ionization and photoelectron peaks. We present the experimental and theoretical investigation of the effects of the strong electromagnetic coupling of two autoionizing states ͑AIS's͒ on the photoionization properties of an atomic system. These effects are observed by probing the ladder system from the ground state of the atom through a weak two-photon transition to the region of the lower AIS. The experimental observation of the modification of the total ionization and partial photoelectron spectra at different wavelengths of the coupling and probe lasers are accurately reproduced by a theoretical analysis which uses a density-matrix approach. Both theory and experiment indicate a strong inhibition of the ionization of the system in the case when both lasers are resonant with the two atomic transitions, while displaying a rapidly varying asymmetry induced as the detuning between the two states and the fields increases. In the extreme case of a large detuning, two separate structures appear as distinct total ionization and photoelectron peaks. The above findings combined with the full theoretical treatment indicate that the phenomena observed are an experimental demonstration of ac Stark splitting between two AIS's..

Two-colour experiments in the gas phase

“…The underlying physics for such doubly optically resonant processes has already been investigated in many theoretical papers (e.g. [40,41,42]), but only one experiment has been performed up to now, and only at very low excitation energies [43]. An illustration of the expected effect of optical coupling between two autoionization states, here 2s2p…”

Investigation of laser induced structures in multiphoton ionization of magnesium

“….) has been given with details elsewhere (see [9]), as well as the density matrix formalism used to calculate the ionization yield. Under the usual approximations (dipole, rotating wave approximations .…”

“…A probe laser couples the 3s ground state to the 3sks and 3skd continua through two-photon absorption, a second laser (coupling laser) couples these continua to the upper 3p3d PM doubly excited state. Such a scheme has been already studied (both experimentally and theoretically) by Karapanagioti et al [8,9], but emphasis was put on the resonant coupling of 3p3d PM and 3p SC autoionizing states. Nevertheless, Karapanagioti et al [9] have shown an experimental spectra (see Fig.…”

“…Such a scheme has been already studied (both experimentally and theoretically) by Karapanagioti et al [8,9], but emphasis was put on the resonant coupling of 3p3d PM and 3p SC autoionizing states. Nevertheless, Karapanagioti et al [9] have shown an experimental spectra (see Fig. 5 in the cited paper) where the coupling laser was tuned far from resonance.…”

Two-electron effects in the multiphoton ionization of magnesium with 400-nm 150-fs pulses

“…The electron energies (reported in table I) are deduced from the energy conservation principle excluding laser induced level shifts. The atomic structure calculations providing the atomic energy levels and the transition cross-sections have been described in detail in a precedent paper [15]. The energies and wave-functions are computed using a frozen-core configuration interaction (CI) procedure.…”