Surface ionization of metastable calcium atoms

I Bucay,A Helal,M G Raizen

doi:10.1063/5.0005895

Abstract

We report on an experimental study of surface ionization of metastable calcium atoms on a hot polycrystalline tungsten surface in vacuum. We implemented a hollow-cathode discharge to excite a fraction of calcium atoms in an atomic beam to metastable states and collected the resulting calcium ions. We observed that metastable calcium atoms are ionized with a significantly greater efficiency than ground-state atoms, and the results suggest that virtually every metastable atom impacting the hot surface is ionized. These results demonstrate the potential of metastable atom surface ionization as a means of enriching calcium isotopes for applications in medicine, metrology, and fundamental science.

Highlights

IntroductionThe efficiency of surface ionization is given by β = α/(1 + α) and is defined as the ratio of ions emitted from the surface to the total flux of atoms incident on the surface
When atoms with an ionization energy I are adsorbed on a metal surface with an electronic work function Φ, the degree of ionization of the atom, α is given by the Saha-Langmuir equation,1 α = ni = gi e−(I−Φ)/kBT, (1)n0 g0 where ni is the flux of surface ions emitted from the surface, n0 is the flux of desorbed neutrals, g0 and gi are the statistical weights of the atomic and first ionic ground states, respectively, and T is the temperature of the heated metal surface
With an appropriately selected metal surface, the surface ionization efficiency may be significantly higher for the excited atoms

Summary

Introduction

The efficiency of surface ionization is given by β = α/(1 + α) and is defined as the ratio of ions emitted from the surface to the total flux of atoms incident on the surface.. We demonstrate that metastable atoms undergo surface ionization with a greater efficiency than ground-state atoms. In alkaline earth and alkaline earth-like systems, this phenomenon has a direct application in atomic clocks, wherein a single frequency-stabilized laser is used to pump a narrow clock transition and the selective surface ionization of the resultant metastable atoms may yield a markedly higher signal-to-noise ratio than conventional atomic clock configurations.. The ability to selectively ionize excited atoms on a metal surface can be exploited for isotopeselective detection and isotope enrichment: atoms of the desired isotope may be optically pumped by a resonant laser to an excited state. With an appropriately selected metal surface, the surface ionization efficiency may be significantly higher for the excited atoms.

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