Impact broadening of alkali Rydberg levels in pure and mixed alkali vapours

Abstract

We have measured the broadening, and in one case also the shift, of alkali nS and nD Rydberg levels by alkali perturbers (Cs by Cs, Rb by Cs and K, and K by Rb) applying the Doppler-free two-photon technique and thermionic detection. Taking into account recent experimental data for the self-broadening of K and Rb Rydberg levels we found that for low principal quantum numbers n the broadening data of the levels are in agreement within the limits of experimental uncertainty in the pure and mixed cases. For high n we could establish that the broadening of the levels is governed by the perturber-valence electron and the perturber-ion core interaction. With increasing n the broadening rates are only dependent on the sort of perturber. As reported recently for Rb-Rb and K-K, oscillations in the broadening data as a function of n were also observed for Cs-Cs and in the mixed vapours. Our results do not support recent theories which describe the oscillations in terms of resonances in the scattering of the quasifree valence electron on the perturber atom. In a classical absorption experiment oscillations in the self-broadening and shift of the Cs principal series lines discovered by Mazing and Serapinas were found to be due to satellite structures which are merged in non-Lorentzian line wings.

Collisional broadening of Rydberg atoms perturbed by ground-state sodium atoms

“…In contrast with the impulse-approximation approach [6], our theory gives nontrivial dependence of the broadening cross sections on the sort of the perturbed atom, the feature which was emphasized in the experimental paper [ 1 ]. One of the important parameters of our theory is the fractional part of the quantum defect which is substantially different for the Na and Cs atoms (0.3 for Na and 0.05 for Cs).…”

“…The 3p-resonance in lowenergy electron scattering by alkali-metal atoms plays a decisive role in the mechanism of oscillations, although its role is not so simple as originally suggested [6]. The model approach [7] allowed us to perform calculations [8] The experiments [1,2] were performed for heavy alkalies (K, Rb, and Cs). Low-energy electron scattering by these atoms has many general features [3], including very large cross sections and the 3p-resonance in the region around 0.01-0.02 eV.…”

“…Experimental measurements [1,2] of collisional broadening of Rydberg states by alkali perturbes have created great theoretical interest in the collisions between Rydberg and ground-state alkali-metal atoms. Calculations [3][4][5] performed in the impulse approximation have explained the general features of these processes and the large values of the broadening cross sections.…”

Precise quantum defects of nS, nP and nD Levels in Cs I

“…Cs vapour pressures of about 5 mTorr were used throughout the experiments. The corresponding Cs number density of 1 x 1014cm -3 induces self-pressure shifts for the highest lying nS and nD levels (n~30) of about -7MHz [17]. The self-shift corrections were taken into account when determining the unperturbed energy positions of the relevant Cs states.…”

Experimental Verification of Minima in Excited Long-Range Rydberg States ofRb2

“…Different models proposed and discussions held at conferences dealing with spectral line shapes have not to date produced satisfactory explanations. Moreover, the unexpected oscillations of experimental line shift and impact broadening parameters, in their dependence on the effective quantum number for alkali Rydberg line series, are still without adequate explanation (see [18] and references therein).…”