Electron interferometry via phase-contrast microscopy, holography, or picodiffraction can provide a direct visualization of the static electric and magnetic fields inside or around a material at subatomic precision, but understanding the electromagnetic origin of light-matter interaction requires time resolution as well. Here, we demonstrate that pump-probe electron diffraction with all-optically compressed electron pulses can capture dynamic electromagnetic potentials in a nanophotonic material with sub-light-cycle time resolution via centrosymmetry-violating Bragg spot dynamics. The origin of this effect is a sizable quantum mechanical phase shift that the electron de Broglie wave obtains from the oscillating electromagnetic potentials within less than 1 fs. Coherent electron imaging and scattering can therefore reveal the electromagnetic foundations of light-matter interaction on the level of the cycles of light.

通过相差显微镜，全息术或皮衍射技术进行的电子干涉测量可以以亚原子精度直观显示材料内部或周围的静电场和磁场，但是了解光物质相互作用的电磁起源也需要时间分辨。在这里，我们证明了具有全光压缩电子脉冲的泵浦探针电子衍射可以通过中心对称性违反布拉格点动力学，以亚光周期时间分辨率捕获纳米光子材料中的动态电磁势。这种效应的起因是电子德布罗意波从小于1 fs的振荡电磁势中获得的相当大的量子机械相移。