Field ionization of Rydberg atoms for high-brightness electron and ion beams

Abstract

We present an ionization mechanism for use in a cold atom electron source with the goal of producing highly monochromatic electron beams. We experimentally produce a map of the Stark states of 85 Rb below the ionization threshold and identify states that undergo selective field ionization. The properties of an electron beam produced by field-assisted ionization of such states are quantified. A theoretical framework is established to predict the improvement to beam quality when ionization is conducted above the ionization threshold, where ionization conditions are typically more favorable than below the threshold. Calculations suggest that selective ionization of Rydberg states may offer a pathway to the production of high-brightness, highly monochromatic ion and electron beams.

State-selective electric-field ionization of Rydberg positronium

“…Atoms and molecules excited to Rydberg states can be manipulated using inhomogeneous electric fields [4], and are of interest in a variety of experimental areas (see, e.g., Refs. [5][6][7][8][9]).…”

Time-resolved brightness measurements by streaking

“…(3) and the analysis of the results of a particle tracking simulation of the experiment. Electron bunches produced by field ionization are known to have a duration of order 10 μs as the electrons slowly tunnel across the barrier formed by the Stark-shifted Coulomb potential [38], whereas bunches produced from above-threshold direct ionization had a duration determined by the blue ionization laser pulse duration of 5 ns.…”

“…1) photoionization of a cloud of lasercooled rubidium occurs between two accelerator electrodes, separated by 50 mm. Photoionization was performed with a two-color ionization scheme with a red 780 nm continuous laser to excite from the ground state to an intermediate state and a wavelength-tunable blue 460-490 nm 5 ns-duration pulse laser was used to excite from the intermediate state directly to the ionization continuum or to a high-lying Rydberg state which, due to the accelerating field, is above the Stark-shifted ionization threshold [22,38].…”

Perturbed field ionization for improved state selectivity

“…ample, quantum control of the electron's pathway to ionization could be useful for applications such as producing an electron beam by ionizing Rydberg atoms [33]. It is desirable for the electron beam to have a small spread in energy [34,35], which could be evolved using a GA.…”