Attosecond Transient Absorption in Dense Gases: Exploring the Interplay between Resonant Pulse Propagation and Laser-Induced Line Shape Control

TL;DR

This paper explores how resonant pulse propagation and laser-induced phase shifts affect XUV spectral lineshapes in dense helium gases, revealing complex interplay in both frequency and time domains.

Contribution

It provides a combined experimental and theoretical analysis of lineshape modifications in dense gases, highlighting the interplay between pulse propagation and phase control beyond single atom responses.

Findings

Spectral lineshapes are significantly affected by collective interactions.

IR-induced phase shifts modify the spectral and temporal profiles of XUV pulses.

Propagation distance influences the evolution of absorption features.

Abstract

We investigate the evolution of extreme ultraviolet (XUV) spectral lineshapes in an optically-thick helium gas under near-infrared (IR) perturbation. In our experimental and theoretical work, we systematically vary the IR intensity, time-delay, gas density and IR polarization parameters to study lineshape modifications induced by collective interactions, in a regime beyond the single atom response of a thin, dilute gas. In both experiment and theory, we find that specific features in the frequency-domain absorption profile, and their evolution with propagation distance, can be attributed to the interplay between resonant attosecond pulse propagation and IR induced phase shifts. Our calculations show that this interplay also manifests itself in the time domain, with the IR pulse influencing the reshaping of the XUV pulse propagating in the resonant medium.