Attosecond dynamics through a Fano resonance: Monitoring the birth of a photoelectron

Abstract

Esta es la versión de autor del artículo publicado en: This is an author produced version of a paper published in:Science 354(6313) (2016): 734-738 DOI: http://dx.doi.org/10.1126/science.aah5188 Copyright: © 2016 American Association for the Advancement of ScienceEl acceso a la versión del editor puede requerir la suscripción del recurso Access to the published version may require subscription However, the rapidity of electron dynamics on the attosecond timescale has precluded their complete measurement in the time domain. Here, we demonstrate that spectrally-resolved electron interferometry reveals the amplitude and phase of a photoelectron wavepacket created through a Fano autoionizing resonance in helium. Replicas obtained by two-photon transitions interfere with reference wavepackets formed through smooth continua, allowing the full temporal reconstruction, purely from experimental data, of the resonant wavepacket released in the continuum. This in turn resolves the buildup of the autoionizing resonance on attosecond timescale. Our results, in excellent agreement with ab initio time-dependent calculations, raise prospects for both detailed investigations of ultrafast photoemission dynamics governed by electron correlation, as well as coherent control over structured electron wave-packets.One Sentence Summary: By monitoring the decay of an excited atom in real time, we reconstruct how photoelectron wavepackets are born and morph into asymmetric Fano profiles. Main Text:Tracking electronic dynamics on the attosecond (as) timescale and Ångström (Å) lengthscale is a key to understanding and controlling the quantum mechanical underpinnings of physical and chemical transformations (1). One of the most fundamental electronic processes in this context is photoelectron emission, the dynamics of which are fully encoded in the released electron wavepacket (EWP) and the final ionic state. The development of broadband coherent sources of attosecond pulses has opened the possibility of investigating these dynamics with attosecond resolution. On such a short timescale, few techniques (2-5) are able to provide access to both spectral amplitude and phase. The spectral derivative of the phase, the group delay, is a practical quantity for describing general wavepacket properties reflecting the ionization dynamics.

Photoionization using the xchem approach: Total and partial cross sections of Ne and resonance parameters above the 2s22p5 threshold

“…Over the past decades, the breakthroughs produced in the generation of ultrashort pulses in a broad range of the electromagnetic spectrum, from near-infrared (NIR) femtosecond pulses to extreme ultraviolet (XUV) and x-ray attosecond ones, have provided us with the tools to observe and control electron dynamics in a variety of different scenarios, relevant in physics, chemistry, and biology [1][2][3][4][5][6][7][8][9]. XUV and x-ray pulses are able to ionize atoms and molecules by absorption of a single photon.…”

Attosecond delays in laser-assisted photodetachment from closed-shell negative ions

“…Temporal characterization of attosecond pulses, which requires determination of the spectral phase of the XUV field, can be performed by laser-assisted photoionization [4,5]. More recently, this type of experiments have been used for spectral phase determination of photoelectrons from autoionizing states [6,7] and for the measurement of relative time delays in laser-assisted photoionization from different initial states in solids [8] and atoms [9][10][11]. Relative time delays have also been measured between different atomic species [12][13][14], between single and double ionization [15], between different angles of photoemission [16] and between the ion ground state and shake-up states [17].…”

Watching the emergence of a Fano resonance in doubly excited helium

“…A complementary study by an independent team of researchers allowed to observe the formation of the Fano resonance in the photoelectron spectrum of the very same transition, which has been reported simultaneously [11].…”