Ultrafast Measurement and Control of Excited-State Dynamics Using Nonlinear Spectroscopy in the Extreme-Ultraviolet Regime

Abstract

The advent of ultrafast nonlinear spectroscopy with weak extreme-ultraviolet (XUV) and strong-field near-infrared (NIR) pulses has enabled investigations of electronic processes in atomic and molecular systems with femtosecond and attosecond resolution. Conventional XUV-NIR attosecond transient absorption (ATA) and multi-wave mixing (MWM) spectroscopies have successfully probed coherent electron dynamics in a wide range of quantum systems. However, these optical setups are often limited by the commensurate nature of the harmonic XUV pump and the driving NIR probe. In this work, we enhance the versatility of these techniques by using optical parametric amplification to generate tunable infrared (IR) pulses. This approach allows us to adjust the frequencies of the XUV and IR pulses independently of each other. To demonstrate the power of tunable ATA and MWM schemes, we apply these techniques to study and manipulate laser-induced couplings and autoionizing resonances embedded in the continuum of polyelectronic systems. We begin by investigating the degeneracy between autoionizing bright and light-induced states (LIS) in argon, which leads to the formation of entangled light-matter states known as polaritons. By tuning the IR pulse parameters we demonstrate control over polaritonic evolution and their decay pathways. In the next study, we use the incommensurate IR pulse to drive resonant background-free wave-mixing processes to probe quantum beats that arise from coherent electronic superpositions of singly- and doubly-excited states in krypton. Finally, we discuss the extension of these techniques to molecular systems and macroscopic propagation regimes. Our results further the understanding of autoionization (AI) dynamics in multielectron systems and demonstrate novel methods for the optical measurement and control of excited-state dynamics in the continuum.