Non resonant atom photoionization by intense fields with Raman processes

Gerd Leuchs, G. Alber, Stuart James Smith

Ekaterina A. Volkova, A. M. Popov, Olga V. Tikhonova

The process of resonant multiphoton ionization of a hydrogen atom in the ground 1 s state is studied by direct numerical integration of the nonstationary Schrödinger equation for a quantum system in an electromagnetic field. The dependence of photoionization probability on the radiation intensity is found to be nonmonotonic. It is established that the minima of ionization correspond to multiphoton resonances between the ground state and one of the excited (Rydberg) atomic states perturbed by the laser field. It is shown that ionization is suppressed due to rearrangement of Rydberg states in a strong electromagnetic field and is accompanied by efficient Raman Λ transitions, which connect a set of closely lying Rydberg states via the continuum.

M. Marinescu, H. R. Sadeghpour, A. Dalgarno

Two-color two-photon photoionization of hydrogen and alkali atoms is presented. The method based on a perturbation expansion is valid for low to moderately intense radiation fields. Three processes are considered leading to the photoionization. For the first process both photons are below threshold, and for the second process one photon is above the threshold with an energy less than the final energy of the photoelectron. The last process is identical to the continuum Raman (Compton) scattering where the first photon is absorbed high in the continuum and the second low energy photon is scattered. Photoionization cross sections of hydrogen and the alkali atoms are given as functions of the first photon energy and the photoelectron energy.

J. B. West

L. R. Brewer, Fritz Buchinger, Martin Ligare +1 more

We have measured the resonance-enhanced four-photon ionization of atomic hydrogen. The degenerate four-photon process occurs via a three-photon resonance between the 1s and the 2p levels, with subsequent one-photon ionization near threshold. We have studied the highly asymmetric resonance-enhanced profile, i.e., the photoion yield as a function of laser detuning from three-photon resonance between the 1s and 2p levels. In particular, we have determined the width, shift, peak, and asymmetry of the profile as a function of laser intensity. The experimental results are compared to theoretical models. These models involve both the properties of the atom in an intense near-resonant radiative field, and a detailed model for the multimode laser field, particularly the field fluctuations due to mode beating. The asymmetric resonance-enhanced photoionization profile is well reproduced by both a random-phase and a chaotic-light model.

J. M. Bizau, D. Cubaynes, F. J. Wuilleumier