The subcycle interaction of light and electrons has been one of the key frontiers in free-electron lasers, attosecond science and dynamical investigation of matter. Capturing the underlying subcycle dynamics of electrons with an optical field promises fascinating vistas with unprecedented temporal resolution. Yet the rigorous synchronization requirement has kept its realization out of reach. Here, by direct spatial observation of periodic electron bunch fringes, we demonstrate a laser streaking concept for revealing the dynamics of free electrons emitted from a plasma mirror under sub-relativistic laser intensity. Field-induced electron beam deflection demonstrates subcycle charge dynamics with a streaking speed of ~60 μrad as⁻¹. This provides us with an attosecond-resolution metrology to obtain more direct evidence about the light-field-induced electron dynamics in the plasma mirror. Our results offer unprecedented characterization of attosecond dynamics and open the way to extensive experimental investigations of the interaction of attosecond electrons with intense lasers.

光与电子的子周期相互作用一直是自由电子激光器，阿秒科学和物质动力学研究的关键领域之一。用光场捕获电子的潜在子循环动力学有望以前所未有的时间分辨率吸引人的远景。但是严格的同步要求使它的实现遥不可及。在这里，通过对周期性电子束条纹的直接空间观察，我们展示了激光划痕的概念，用于揭示在亚相对论激光强度下从等离子体镜发射的自由电子的动力学。场致电子束偏转以^-1的〜60μrad的斑纹速度显示了子周期电荷动力学。这为我们提供了一个阿秒分辨率的度量衡，以获取有关等离子镜中光场感应电子动力学的更直接证据。我们的结果提供了对阿秒动力学的前所未有的表征，并为进行阿秒电子与强激光相互作用的广泛实验研究开辟了道路。