Abstract

Few pioneering experiments demonstrated that clocking the time interval between the pump radiation and the optical response of a system with attosecond resolution enables unprecedented physical insights [1]. For example, it allows the unveiling of elusive and, so far, little-known physical phenomena occurring on the sub-femtosecond time scale, such as the interplay between intra-band motion and inter-band transitions in solids [2] or the effect of correlations on photoemission from atoms [3]. Despite its importance, standard attosecond techniques cannot provide absolute timing information directly. The most used strategy consists in performing a simultaneous attosecond streaking measurement [4] and extracting the pump vector potential either from its center-of-mass [5] or from a reconstruction of the trace [6]. Unfortunately, neither approaches are reliable and precise. The former is strongly influenced by the temporal structure of the radiation, failing when the pulses are not isolated. Instead, the latter does not allow unambiguously relating the reconstructed time axis with the experimental delay axis.

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