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

Abstract

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

Comparative analysis of recirculating and collimating cesium ovens

“…One goal being to produce an intense ion or electron beam once ionized. [11][12][13][14] Similar goals for other atoms are pursued in many groups, for instance, Ca, 15 Sr, 16,17 Yb, 18 Ba, 19 Li, 4 and Rb. 20 A systematic study on any atom might thus be useful for the atomic physics community as a whole.…”