Cesium Rydberg-state ionization study by three-dimensional ion-electron correlation: Toward a monochromatic electron source

We study the excitation and ionization of cesium Rydberg states in an electric field ($\ensuremath{\approx}\phantom{\rule{0.16em}{0ex}}2200\phantom{\rule{4pt}{0ex}}\mathrm{V}/\mathrm{cm}$) near classical field-ionization threshold ($\ensuremath{\approx}\ensuremath{-}280\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ binding energy) by three-dimensional (3D) ion-electron coincidence spectroscopy. Cesium atoms are produced effusive oven excited with lasers to Stark-shifted or directly ionized. Using a double time-of-flight setup we record 3D ($X, Y$, time flight) imaging electrons ions. Above-threshold photoionization creates broad images poor electron-ion spatial correlation. Fast ionizing produce very good correlations reveal electric-field map region. Slow show that relatively high atomic velocity is detrimental correlations. Experimental data accurately reproduced detailed Monte Carlo simulations based on Stark maps obtained local-frame transformation (LFT) theory. Agreement between our spectroscopic experiment LFT theory good, better hundreds megahertz accuracy. But, rare particular states, several gigahertz discrepancy found. This can be used select appropriate for creation ion electron beams brightness, correlation, low energy dispersion.