Abstract
Laser-cooled gases offer an alternative to tip-based methods for generating high-brightness ion beams for focused ion beam applications. These sources produce ions by photoionization of ultracold neutral atoms, where the narrow velocity distribution associated with microkelvin-level temperatures results in a very low emittance, high-brightness ion beam. In a magneto-optical trap-based ion source, the brightness is ultimately limited by the transport of cold neutral atoms, which restricts the current that can be extracted from the ion-generating volume. We explore the dynamics of this transport in a 7Li magneto-optical trap ion source by performing time-dependent measurements of the depletion and refilling of the ionization volume in a pulsed source. An analytic microscopic model for the transport is developed, and this model shows excellent agreement with the measured results.
Highlights
Photoionization of laser-cooled atoms offers a novel pathway for constructing high-brightness ion sources.1–7 These sources are fundamentally enabled by the microkelvin temperatures achievable through laser cooling, where atomic ensembles are produced with a very small momentum spread
We explore the dynamics of this transport in a 7Li magneto-optical trap ion source by performing time-dependent measurements of the depletion and refilling of the ionization volume in a pulsed source
When the ionization volume at the center of the magneto-optical trap (MOT) is first exposed to a UV pulse in combination with the IR beam, the instantaneous extracted current is proportional to the ionization probability and the unperturbed local MOT density
Summary
Photoionization of laser-cooled atoms offers a novel pathway for constructing high-brightness ion sources. These sources are fundamentally enabled by the microkelvin temperatures achievable through laser cooling, where atomic ensembles are produced with a very small momentum spread. Photoionization of laser-cooled atoms offers a novel pathway for constructing high-brightness ion sources.1–7 These sources are fundamentally enabled by the microkelvin temperatures achievable through laser cooling, where atomic ensembles are produced with a very small momentum spread. Cold atom ion sources benefit from several advantages over conventional tip-based ion sources, such as access to new ionic species, inherent isotopic purity, insensitivity to contamination, and a low energy spread, which reduces chromatic aberration in ion optical systems and enables source operation at low accelerating voltages. Applications for these new sources are broad, encompassing milling, imaging, spectroscopy, and implantation. A Li magneto-optical trap ion source (MOTIS) has demonstrated high surface sensitivity in imaging, imaging of optical modes in nanophotonic resonators, and utility in studying
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