A Continuous Pump-Probe Experiment to Observe Zeeman Wave Packet Dynamics

TL;DR

This paper demonstrates a novel continuous pump-probe method to observe Zeeman wave packet dynamics in atoms, utilizing a modified COLTRIMS technique to reconstruct ionization timing and track magnetic moment precession in real time.

Contribution

It introduces a new approach combining continuous ionization with data redundancy to monitor atomic Zeeman wave packet evolution in real time.

Findings

Successfully reconstructed ionization timing from continuous measurements.

Observed coherent Larmor precession of atomic magnetic moments.

Extended COLTRIMS technique to include continuous, rather than pulsed, ionization data.

Abstract

In this work, we study the coherent dynamics of an atomic Zeeman wave packet using a continuous pump--probe scheme. A polarized wave packet is generated via few-photon excitation by a femtosecond laser pulse, creating a state with a magnetic moment tilted relative to an external magnetic field. The subsequent Larmor precession of the atoms is probed by continuous ionization in the field of an optical dipole trap (ODT) laser. Photoelectrons and photoions are detected in coincidence using a cold target recoil ion momentum spectrometer (COLTRIMS). While the addition of the ODT enables further cooling of the atomic ensemble, it removes the pulsed timing reference typically used to extract photoelectron momentum distributions in COLTRIMS. Here, we present a method that extends the standard COLTRIMS technique by exploiting redundancy in the measured data to reconstruct the time of ionization. The resulting time-dependent ionization signal reflects the coherent precession of the atomic magnetic moment, enabling real-time access to atomic dynamics on nanosecond timescales.