Nonresonant coherent amplitude transfer in attosecond four-wave-mixing spectroscopy

Attosecond four-wave mixing (FWM) spectroscopy using an extreme ultraviolet (XUV) pulse and two noncollinear near-infrared (NIR) pulses is employed to measure Rydberg wave packet dynamics resulting from XUV excitation of a 3s electron in atomic argon into a series of autoionizing 3s-1 np Rydberg states similar to 29 eV. The emitted signals from individual Rydberg states exhibit oscillatory structure and persist well beyond the expected lifetimes of the emitting Rydberg states. These results reflect substantial contributions of longer-lived Rydberg states to the FWM emission signals of each individually detected state. A wave packet decomposition analysis reveals that coherent amplitude transfer occurs predominantly from photoexcited 3s-1(n + 1)p states to the observed 3s-1 np Rydberg states. The experimental observations are reproduced by time-dependent Schrodinger equation simulations using electronic structure and transition moment calculations. The theory highlights that coherent amplitude transfer is driven nonresonantly to the 3s-1 np states by the NIR light through 3s-1 (n + 1)s and 3s-1(n-1)d dark states during the FWM process.

Automated summary

Attosecond four-wave mixing (FWM) spectroscopy is used to study the Rydberg wave packet dynamics in argon atoms. The experiment shows that the emitted signals from individual Rydberg states have oscillatory structure and persist beyond the expected lifetimes. The coherent amplitude transfer is driven by nonresonant NIR light through dark states during the FWM process.