Comment on "Comment on Attosecond electron microscopy and diffraction"

Abstract: Over the past few decades, following the first demonstration of ultrafast electron microscopy, numerous research groups have focused on achieving attosecond temporal resolution in electron microscopy with the goal of imaging electron and atomic motion. Recently, several studies have claimed to achieve attosecond temporal resolution in imaging(1-3). These claims are based on the generation of attosecond electron pulse trains. However, in typical time-resolved measurements used to capture dynamic processes in real-time, the temporal resolution is determined by the envelope of the pulse train. The reliance of using attosecond electron pulse trains fails to account for the distinct temporal resolution advantages enabled by our attosecond optical gating, which are absent in the case of using a continuous-wave or long laser pulse. These oversights highlight the limitations of this methodology (1-3) in studying ultrafast phenomena of matter. It is crucial to clarify this distinction to avoid confusion, misinterpretation, and potential miscitations within the community regarding attosecond temporal resolution in electron microscopy and the attosecond imaging of matter dynamics. In contrast, Hui et al. (4) present the first realistic demonstration of attosecond imaging resolution in electron microscopy, enabling the diffraction imaging of electron motion dynamics in graphene. In a commentary by Peter Baum and Claus Ropers, the authors conjecture that the graphene dynamics observed in our time-resolved diffraction experiment (Fig. 5, Hui et al. 2024) (4) is an optical interference artifact or light modulation of electrons effects, similar to what was reported previously (1-3), in addition to raising other technical concerns. In this reply, we are pleased to address these allegations and provide clarifications to resolve the raised technical questions.