Probing and controlling coherent electron wavepackets in ionic systems*

We implement attosecond-resolved transient absorption spectroscopy in a three-pulse scheme: a mid-infrared pump pulse to create ions, an extreme ultraviolet probe pulse, and a control pulse to manipulate electron dynamics. This method enables us to track and control coherent electronic wavepackets in both atomic and molecular ionic systems. In atomic argon, we prepare spin-orbit split ionic ground states and probe them using the 21st and 23rd harmonics of the XUV field. We observe quantum interference between transitions to a common final state 5d_1/2, producing oscillations with a 23 fs beat period. Similarly, transitions to 4d_3/2 exhibit interference patterns out of phase with the first. Introducing a control pulse interrupts these fast oscillations, inducing slower 50 fs beats accompanied by AC Stark shifts, demonstrating active control over spin-orbit quantum beats and coherent ionic dynamics. In molecular systems, we investigate iodomethane, ionized by strong-field MIR pulses and probed with XUV photons (45–60 eV), driving transitions such as 4d(I)→6p_e spin-orbit split channels. We observe nuclear wavepacket motion through 26 fs oscillations lasting ~200 fs, revealing ultrafast charge redistribution and electron-nuclear coupling in the ionized molecule. A control pulse introduced at 700 fs reinitiates these oscillations for a few cycles, demonstrating dynamic control over nuclear and electronic coherence.