Stroboscopic visualization of nuclear or electron dynamics in atoms, molecules or solids requires ultrafast pump and probe pulses and a close to perfect synchronization between the two. We have developed a 3 MeV ultrafast electron diffraction (UED) probe technology that nominally reduces the electron bunch duration and the arrival time jitter to the subfemtosecond level. This simple configuration uses a radiofrequency photogun and a 90° achromatic bend and is designed to provide effectively jitter-free conditions. Terahertz streaking measurements reveal an electron bunch duration of 25 fs, even for a charge as high as 0.6 pC, and an arrival time jitter of 7.8 fs, the latter limited by only the measurement accuracy. From pump–probe measurements of photoexcited bismuth films, the instrument response function was determined to be 31 fs. This pioneering jitter-free technique paves the way towards UED of attosecond phenomena in atomic, molecular and solid-state dynamics.

原子，分子或固体中的核或电子动力学的频闪观测需要超快的泵浦和探测脉冲，以及两者之间的接近完美的同步。我们已经开发了3 MeV超快电子衍射（UED）探针技术，该技术名义上可将电子束持续时间和到达时间抖动降低到亚飞秒级。这种简单的配置使用了射频光枪和90°消色差弯头，旨在有效地提供无抖动的条件。太赫兹条纹测量显示，即使电荷高达0.6 pC，电子束持续时间也为25 fs，到达时间抖动为7.8 fs，后者仅受测量精度的限制。通过光激发铋薄膜的泵浦探针测量，仪器响应函数被确定为31 fs。