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arXiv:2608.09549

Resonant photoionization dynamics during optical trapping of lithium atoms

K. Foster, S. Majumdar, D. Fischer

Published Aug 10, 2026• 0 citations
arXivHTMLPDF

Abstract

Photoionization induced by trapping and auxiliary laser fields is an inherent feature of many laser-cooling and optical trapping experiments, yet its microscopic dynamics are rarely investigated directly. In this work, we employ a reaction microscope implementing an event-by-event photoionization time retrieval technique to extend momentum-resolved photoelectron spectroscopy to continuous-wave laser--atom interactions. We investigate low-intensity multicolor photoionization of laser-cooled lithium atoms confined in an all-optical trap. Complete three-dimensional electron momentum distributions and kinetic-energy spectra recorded for different laser wavelengths and polarization configurations identify resonant excitation of the $5p$ and $5f$ states and reveal an additional ionization channel following spontaneous decay from the $5f$ to the $4d$ state. A pronounced polarization dependence of the photoionization yield is explained by magnetic-sublevel selection rules and the coherent interference of different virtual excitation pathways. These results demonstrate that reaction microscopy combined with event-by-event time reconstruction provides a powerful approach for investigating microscopic electronic dynamics in laser-cooled atomic systems and offers new insight into photoionization processes occurring during optical trapping.

DOI
10.48550/arxiv.2608.09549

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In this work, we study the coherent dynamics of an atomic Zeeman wave packet using a continuous pump-probe scheme. A polarized Zeeman wave packet is created in laser-cooled lithium atoms via few-photon excitation by a femtosecond laser pulse, producing a state with a magnetic moment tilted relative to an external magnetic field. The subsequent Larmor precession of the atomic magnetic moment is probed via continuous ionization by an optical dipole trap (ODT) laser. The resulting ionization fragments---photoelectrons and photoions---are detected in coincidence using a cold target recoil ion momentum spectrometer (COLTRIMS). While the ODT facilitates further cooling of the atoms, its continuous-wave laser field does not provide the pulsed timing reference typically required to extract photoelectron momentum distributions in COLTRIMS. Here, we present an extension of the standard COLTRIMS technique that exploits redundancies in the measured data to reconstruct the ionization time. The resulting time-dependent ionization signal reveals the coherent precession of the atomic magnetic moment, enabling real-time access to atomic dynamics on nanosecond timescales.
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