# Phase-Resolved Two-Dimensional Spectroscopy of Electronic Wavepackets by Laser-Induced XUV Free Induction Decay

## TL;DR

This paper introduces a phase-resolved, background-free method to study ultrafast electronic wavepacket dynamics in the extreme ultraviolet range using laser-induced free induction decay, without requiring an EUV excitation pulse.

## Contribution

It presents a novel technique combining multiphoton excitation and heterodyne detection to analyze electron dynamics and dephasing in real-time without background interference.

## Key findings

- Direct measurement of laser-induced dephasing of EUV emission
- Revealed the influence of collisions on relaxation processes
- Demonstrated control over emission amplitude and phase

## Abstract

We present a novel time- and phase-resolved, background-free scheme to study the extreme ultraviolet dipole emission of a bound electronic wavepacket, without the use of any extreme ultraviolet exciting pulse. Using multiphoton transitions, we populate a superposition of quantum states which coherently emit extreme ultraviolet radiation through free induction decay. This emission is probed and controlled, both in amplitude and phase, by a time-delayed infrared femtosecond pulse. We directly measure the laser-induced dephasing of the emission by using a simple heterodyne detection scheme based on two-source interferometry. This technique provides rich information about the interplay between the laser field and the Coulombic potential on the excited electron dynamics. Its background-free nature enables us to use a large range of gas pressures and to reveal the influence of collisions in the relaxation process.