Forced field ionization of Rydberg states for the production of monochromatic beams

Abstract

We study Rydberg ionization in an electric field in order to produce monochromatic ion and electron beams. We present an experimental study of the photoexcitation and ionization of high quantum defect states, using excitation from the 7s state in cesium to Rydberg states in the presence of a uniform electric field. Such states can exhibit complex ionization behavior, for instance, highly localized growth in the ionization rate due to interference effects. The data are well reproduced by WKB quantum-defect and frame transformation methods with no adjustable parameters. This indicates that large changes in the Rydberg ionization rate from small changes in electric field are possible when a nearly stable state crosses a more unstable state. A fast variation of the ionization rate with electric field allows for the production of beams with very low energy dispersion. We develop a simple two-level model to predict the voltage and spatial resolution that would occur when atoms are prepared in a state with such sharp ionization in electric field. This confirms that Rydberg forced ionization in an electric field presents a pathway for the production of highbrightness, highly monochromatic ion and electron beams.

Ionization spectra of highly Stark-shifted rubidium Rydberg states

“…Furthermore, this opens up the possibility to tune a coupling between ionizing and non-ionizing states by the external electric field. This way of tailoring the ionization process is highly useful for the design of sources of cold ions and electrons for microscopy purposes [13][14][15][16]. Moreover, a precise knowledge of these ionization spectra opens new perspectives for experiments incorporating Rydberg atoms near surfaces, where static electric fields arise due to adsorbates [17][18][19][20].…”

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.…”

“…When the end of the perturbation occurs after ionization, the fitness increase is ≈0. 35. But if t f is decreased to 1000 ns or less, the fitness increase drops off to ≈0.15.…”

Improving the state selectivity of field ionization with quantum control

“…This optimization technique may be useful for other goals as well. For example, the production of high-brightness, monochromatic electron beams using field ionized Rydberg atoms may benefit from the addition of an optimized perturbation to the ionizing field [36][37][38].…”