Abstract
Realistic attosecond wave packets have complex profiles that, in dispersive conditions, rapidly broaden or split into multiple components. Such behaviors are encoded in sharp features of the wave packet spectral phase. Here, we exploit the quantum beating between one- and two-photon transitions in an attosecond photoionization experiment to measure the photoelectron spectral phase continuously across a broad energy range. Supported by numerical simulations, we demonstrate that this experimental technique is able to reconstruct sharp fine-scale features of the spectral phase, continuously as a function of energy and across the full spectral range of the pulse train, thus beyond the capabilities of existing attosecond spectroscopies. In a proof-of-principle experiment, we retrieve the periodic modulations of the spectral phase of an attosecond pulse train due to the individual chirp of each harmonic.
Highlights
Attosecond photoionization time delays provide a precise timing of electronic motion in atoms [1,2,3], molecules [4,5], and solids [6,7,8,9]
We demonstrate that the quantum beat between one- and two-photon transitions, formerly referred to as 1-2 quantum beat [26,27,28,29], together with angle-resolved electron spectroscopy, provides direct access to complex structures in the spectral phase of the photoionized electron wave packets, which, to the best of our knowledge, are, otherwise, accessible only by complete pulse reconstruction techniques
The experiment is carried out resembling the RABBITT protocol and using an XUV-attosecond pulse train (APT) with spectrally broad high harmonics
Summary
Attosecond photoionization time delays provide a precise timing of electronic motion in atoms [1,2,3], molecules [4,5], and solids [6,7,8,9]. Defined as group delay difference between two electron wave packets, they set benchmarks for the most advanced quantum simulations [10,11,12]. As group delays are given by the first-order expansion of the spectral phase φ(E ), they cannot characterize the full wave packet evolution. Dynamical aspects more complex than a simple delay, such as changes in the wave packet envelope shape, can only be reconstructed if the energy-dependent spectral phase is measured in full. Most experimental techniques currently used to characterize photoionization phases can retrieve only the average value of the group delay across a broad energy range, e.g., the whole attosecond pulse bandwidth in streaking measurements [1,17,18], or at discrete energies spaced by twice the probe frequency, in the RABBITT (reconstruction of attosecond beatings by interference of two-photon transitions) scheme
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