Streaking and Wigner time delays in photoemission from atoms and surfaces

TL;DR

This paper explores the relationship between Wigner and streaking time delays in photoemission from atoms and surfaces, revealing how material properties influence these delays and their interpretation.

Contribution

It provides a theoretical analysis connecting Wigner and streaking delays, highlighting their dependence on surface properties and ionic potentials in photoemission.

Findings

Wigner and streaking delays are equivalent for ideal surfaces with zero IR skin depth.

Differences between delays depend on IR skin depth in solids.

Atomic delays vary with ionic potential range.

Abstract

Streaked photoemission metrology allows the observation of an apparent relative time delay between the detection of photoelectrons from different initial electronic states. This relative delay is obtained by recording the photoelectron yield as a function of the delay between an ionizing ultrashort extended ultraviolet (XUV) pulse and a streaking infrared (IR) pulse. Theoretically, photoemission delays can be defined based on i) the phase shift the photoelectron wavefunction accumulates during the release and propagation of the photoelectron (``Wigner delay") and, alternatively, ii) the streaking trace in the calculated photoemission spectrum (``streaking delay"). We investigate the relation between Wigner and streaking delays in the photoemission from atomic and solid-surface targets. For solid targets and assuming a vanishing IR-skin depth, both Wigner and streaking delays can be interpreted as an average propagation time needed by photoelectrons to reach the surface, while the two delays differ for non-vanishing skin depths. For atomic targets, the difference between Wigner and streaking delays depends on the range of the ionic potential.