Wigner time delay in atomic photoionization

Abstract

For over a century since the Nobel prize winning work by Einstein (1905), atomic photoionization was thought to be an instantaneous process. Recent experimental progress in ultrashort laser pulse generation has allowed to resolve this process in time. The concept of time delay introduced by Wigner (1955) in particle scattering appears to be central to the time resolution of photoionization. In this review, we examine the fundamental concepts of time-respolved atomic ionizataion processes. We will follow the recent literature and show how the initial disagreements between theory and experiment, which persisted for nearly a decade, were finally reconciled. We will also outline the exciting prospects of this field driven by modern experimental and computational technologies.

Wigner time delay in photoionization: a 1D model study

“…Figure 4 illustrates the case of a narrow energy bandwidth relative to the width of the resonance in δ ′ o (E), which is the validity domain of section 3.1, as shown in the inset of figure 4(a). One can see in (a) that the non-free wavepacket far away from the potential is simply a Gaussian with a delayed peak relative to the free wavepacket peak, in agreement with equation (24). In this case, the space delay information inferred from either the difference of the two Gaussian peaks positions (figure 4(a)) or the B coefficient in the straight line fit of the non-free ⟨x⟩ curve (figure 4(b) inset) is identical.…”

“…Equation (24) shows an initial evidence of a delay time contained in |ψ R (t)⟩ given directly by the odd phaseshift energy derivative. Although the part of the incoming-wave scattering state |ψ R E ⟩ that survives at t → ∞ when put into the wavepacket integral (i.e.…”

“…This intensely triggered several studies to apply contemporary theoretical approaches such as the time-dependent R-matrix method and the randomphase approximation in order to explain these time delay measurements [4][5][6][7][8][9][10]. However, discrepancies between theory and experiment remained until they were resolved by refined experimental measurements in 2017 [11] and 2021 [12] as explained in [13]. Moreover, Saalmann and Rost [14] questioned the measurements of Schultze et al [2] and theoretically derived the specific conditions under which streaking shifts truly measure Wigner-Smith time delays.…”

“…The EWS time delay formalism has been extended to include photoionization and photodetachment by Deshmukh et al [22,23] in a treatment that uses the time-reversal conjugate symmetry between incoming-and outgoing-wave solutions. Apparently contesting that point of view, a recent preprint by Fetić et al [24] asserts that the Wigner time delay cannot be inferred from the liberated particle wavefunction, through its phaseshift, and hence cannot be measured in a photoionization setup. Their claim relies primarily on the fact that, in photoionization, the wavepacket of the emitted particle is composed of incomingwave eigenstates of which the part arriving at the detector (the outgoing free-particle or Coulomb-modified plane wave) carries no information about the scattering phases.…”

Attosecond ionization time delays in strong-field physics

“…[105] Generally speaking, attosecond electron dynamics is an important topic in ultrafast science and its study has led to a variety of novel findings. [106] Recently, the temporal resolution of the buildup of Fano resonance, [107,108] chiral photoemission, [109] Auger process, [110,111] and Rabi dynamics [112] has also been achieved. In addition, correlation effects in photoionization of argon [113] and confinement effects in photoionization of argon in C 60 [114] have been studied using the time-dependent density functional theory.…”