On the Width and Density of Highly Excited Atomic Levels in Gases

Linjie Zhang, Zhigang Feng, Jianming Zhao +2 more

We present the explicit dynamics process of Rydberg cesium atoms initially experiencing a repulsive van der Waals (vdW) interaction by measuring the line width and intensity of the Rydberg ionization spectra. The signals of Rydberg atoms and free ions are recorded simultaneously within an initial 3.5 micros delay time between the excitation laser and the ramp electric field. For high-density gases, a rapid decrease of Rydberg atoms and an increase of free ions are observed, which is not found to be the case for low-density gases. The experimental results indicate that superradiance is the main cause of the redistribution of Rydberg atoms from the repulsive potential to the attractive potential for high density, which provides the initial ionization. The corresponding theoretical calculation is also given.

Daniel Kleppner

Haider R. Zaidi

The resonance broadening of a transition between two excited states of a radiator in a high density gas is investigated. The important many body shielding contributions are included to all orders, and the two body correlations for the close collisions are approximately taken into account. Corrections to the line width and shift at moderately high densities are calculated. The results agree with the experimental data for krypton. The density dependence of the width parameter is examined at very high densities also. It is found that this parameter, after reaching a peak value, decreases with further increase in the density. Moreover, the square root dependence of the line widths on the density is not valid over any extended range of gas densities.

A. P. Kazantsev

C. Alden Mead, Hendrik F. Hameka

Dmitry K. Efimov, K. Miculis, Nikolai N. Bezuglov +1 more

Abstract We consider Penning ionization of Rydberg atom pairs as an Auger-type process induced by the dipole–dipole interaction and employ semiclassical formulae for dipole transitions to calculate the autoionization width as a function of the principal quantum numbers, n d , n i , of both atoms. While for symmetric atom pairs with n d = n i = n 0 the well-known increase of the autoionization width with increasing n 0 is obtained, the result for asymmetric pairs is counterintuitive—for a fixed n i of the ionizing atom of the pair, the autoionization width strongly increases with decreasing n d of the de-excited atom. For H Rydberg atoms this increase reaches two orders of magnitude at the maximum of the n d dependence, and the same type of counterintuitive behavior is exhibited also by Na, Rb and Cs atoms. This is a purely quantum-mechanical effect, which points towards existence of optimal (we call them ‘Tom’ and ‘Jerry’ for ‘big’ and ‘small’) pairs of Rydberg atoms with respect to autoionization efficiency. Building on the model of population redistribution in cold Rydberg gases proposed in [1], we demonstrate that population evolution following the initial laser excitation of Rydberg atoms in state n 0 would eventually lead to the formation of such Tom–Jerry pairs with n i > n 0 > n d which feature autoionization widths that are enhanced by several orders of magnitude compared to that of two atoms in the initial laser-excited state n 0 . We also show that in the high-density regime of cold Rydberg gas experiments the ionization rate of Tom–Jerry pairs can be substantially larger than the blackbody radiation-induced photoionization rate.