Continuous pump-probe experiment to observe Zeeman wave-packet dynamics

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.