The Optimal Pair of Rydberg Alkali-Metal Atoms in the Nonsymmetric Penning Ionization Processes

Optics and Spectroscopy - Features of Penning ionization in cold gaseous media of Rydberg alkali-metal atoms have been investigated. In contrast to the hydrogen atom, the corresponding...     

Autoionization of an ultracold Rydberg gas through resonant dipole coupling

We investigate a possible mechanism for the autoionization of ultracold Rydberg gases, based on the resonant coupling of Rydberg pair states to the ionization continuum. Unlike an atomic collision where the wave functions begin to overlap, the mechanism considered here involves only the long-range dipole interaction and is in principle possible in a static system. It is related to the process of intermolecular Coulombic decay (ICD). In addition, we include the interaction-induced motion of the atoms and the effect of multi-particle systems in this work. We find that the probability for this ionization mechanism can be increased in many-particle systems featuring attractive or repulsive van der Waals interactions. However, the rates for ionization through resonant dipole coupling are very low. It is thus unlikely that this process contributes to the autoionization of Rydberg gases in the form presented here, but it may still act as a trigger for secondary ionization processes. As our picture involves only binary interactions, it remains to be investigated if collective effects of an ensemble of atoms can significantly influence the ionization probability. Nevertheless our calculations may serve as a starting point for the investigation of more complex systems, such as the coupling of many pair states proposed in [P.J. Tanner et al., Phys. Rev. Lett. 100, 043002 (2008)].     

Experimental control of excitation flow produced by delayed pulses in a ladder of molecular levels

We study a method for controlling the flow of excitation through decaying levels in a three-level ladder excitation scheme in Na(2) molecules. Like the stimulated Raman adiabatic passage (STIRAP), this method is based on the control of the evolution of adiabatic states by a suitable delayed interaction of the molecules with two radiation fields. However, unlike STIRAP, which transfers a population between two stable levels g and f via a decaying intermediate level e through the interaction of partially overlapping pulses (usually in a Lambda linkage), here the final level f is not long lived. Therefore, the population reaching level f decays to other levels during the transfer process. Thus, rather than controlling the transfer into level f, we control the flow of the population through this level. In the present implementation a laser P couples a degenerate rovibrational level in the ground electronic state X 1Sigma(g)+, v" = 0, j" = 7 to the intermediate level A 1Sigma(u)+, v' = 10, J' = 8, which in turn is linked to the final level 5 1Sigma(g)+, v = 10, J = 9 by a laser S, from which decay occurs to vibrational levels in the electronic A and X states. As in STIRAP, the maximum excitation flow through level f is observed when the P laser precedes the S laser. We study the influence of the laser parameters and discuss the consequences of the detection geometry on the measured signals. In addition to verifying the control of the flow of population through level f we present a procedure for the quantitative determination of the fraction kappa(f) of molecules initially in the ground level which is driven through the final level f. This calibration method is applicable for any stepwise excitation.     

Control of population flow in coherently driven quantum ladders

A technique for adiabatic control of the population flow through a preselected decaying excited level in a three-level quantum ladder is presented. The population flow through the intermediate or upper level is controlled efficiently and robustly by varying the pulse delay between a pair of partly overlapping coherent laser pulses. The technique is analyzed theoretically and demonstrated in an experiment with Na2 molecules.     

Analysis of light-induced diffusion ionization of a three-dimensional hydrogen atom based on the Floquet technique and split-operator method

A stable symplectic scheme for calculating particle trajectories in time-periodic force fields based on the Floquet technique and split-operator method is described. The dynamics of a three-dimensional hydrogen atom under the action of an external linearly polarized microwave electric field is studied in a numerical experiment. Under conditions of the implemented dynamical chaos, features in the evolution of angular momentum L(t) of a Rydberg electron (RE) that do not meet the assumptions of traditional theoretical approaches for describing light-induced diffusion ionization of the RE are revealed.     

Theoretical study of energy transfer in Rb(7S) + Rb(5S) and Rb(5D) + Rb(5S) collisions

We present results of theoretical studies of the non-resonant excitation transfer in Rb(7S) + Rb(5S) and Rb(5D) + Rb(5S) collisions at thermal collision energies. Rb₂ adiabatic molecular terms correlating with the 5S+7S, 5S+5D and 5P+5P states of separated atoms were calculated for internuclear distances R > 20 a.u. using asymptotic approximation. Mechanisms of collisional population and quenching of the 5D state were treated on the basis of the computed molecular terms, and the respective cross-sections were calculated. Theoretical cross-sections are in good agreement with the experimental values at thermal collision energies ( K). Received 13 November 1998 and Received in final form 22 November 1999     

Inelastic cross-sections and natural lifetimes for the 62D3/2, 5/2 and 82S1/2 states of Rb

The results of an experimental study of population dynamics following excitation of [0pt] and [0pt] states of rubidium are reported. Excitation transfer and quenching cross-sections in collisions with ground state rubidium atoms, and natural lifetimes have been measured. The experiment was performed in a vapour cell, using pulsed two-photon excitation and photon counting detection. The analysis of time dependent signals was based on a rate equation model in which transitions induced by thermal radiation have been accounted for. The measurements yielded following results: (1) [0pt] state J-mixing cross-section: [0pt] ; (2) cross-sections for [0pt] excitation transfer process: [0pt] ; (3) quenching cross-sections: [0pt] , [0pt] , [0pt] ; [0pt](4) radiative lifetimes: [0pt] ns, [0pt] ns, [0pt] ns. Received 1st December 1998 and Received in final form 17 May 1999