Effect of photoions on the line shapes of the F\"orster resonance and microwave transitions in cold rubidium Rydberg atoms

TL;DR

This study investigates how photoions cause line broadening in the spectroscopy of cold Rydberg rubidium atoms, demonstrating that removing photoions can significantly narrow resonance lines and improve spectral resolution.

Contribution

It identifies photoions as the main source of line broadening in Rydberg atom spectroscopy and shows that electric field pulses can effectively reduce this broadening.

Findings

Photoions cause 2-3 MHz line broadening in spectra.

Applying electric field pulses narrows resonance lines.

Photoion removal improves spectral resolution.

Abstract

Experiments on the spectroscopy of the F\"orster resonance Rb(37P)+Rb(37P) -> Rb(37S)+Rb(38S) and microwave transitions nP -> n'S, n'D between Rydberg states of cold Rb atoms in a magneto-optical trap have been performed. Under ordinary conditions, all spectra exhibited a 2-3 MHz line width independently of the interaction time of atoms with each other or with microwave radiation, although the ultimate resonance width should be defined by the inverse interaction time. Analysis of the experimental conditions has shown that the main source of the line broadening was the inhomogeneous electric field of cold photoions appeared at the excitation of initial Rydberg nP states by broadband pulsed laser radiation. Using an additional pulse of the electric field, which rapidly removed the photoions after the laser pulse, lead to a substantial narrowing of the microwave and F\"orster resonances. An analysis of various sources of the line broadening in cold Rydberg atoms has been conducted.