The recent development of optical control of electron pulses brings new opportunities and methodologies in the fields of light–electron interaction and ultrafast electron diffraction (UED)/microscopy. Here, by a comprehensive theoretical study, we present a scheme to compress the longitudinal duration of low (⩽1 keV) to medium energy (1–70 keV) electron pulses by the electric field of a THz wave, together with a novel shot-by-shot jitter correction approach by using the magnetic field from the same wave. Our theoretical simulations suggest the compression of the electron pulse duration to a few femtoseconds and even sub-femtosecond. A comprehensive analysis based on typical UED patterns indicates a sub-femtosecond precision of the jitter correction approach. We stress that the energy independence of Coulomb interaction in the compression and the compact structure of THz device lay the foundation of the compression of low energy electron pulses. The combination of the THz compression of the electron pulse and the electron–THz jitter correction opens a way to improve the overall temporal resolution to attosecond for ultrafast electron probes with low to medium energies and high charge number per pulse, and therefore, it will boost the ultrafast detection of transient structural dynamics in surface science and atomically thin film systems.

We observed the ultrafast lattice dynamic in lead selenide (PbSe) quantum dots using ul-trafast electron diffraction. The electron-phonon coupling time constant is about 10 ps, showing no sign of phonon bottleneck.

A thorough understanding of the photocarrier relaxation dynamics in semiconductor quantum dots (QDs) is essential to optimize their device performance. However, resolving hot carrier kinetics under high excitation conditions with multiple excitons per dot is challenging because it convolutes several ultrafast processes, including Auger recombination, carrier− phonon scattering, and phonon thermalization. Here, we report a systematic study of the lattice dynamics induced by intense photoexcitation in PbSe QDs. By probing the dynamics from the lattice perspective using ultrafast electron diffraction together with modeling the correlated processes collectively, we can differentiate their roles in photocarrier relaxation. The results reveal that the observed lattice heating time scale is longer than that of carrier intraband relaxation obtained previously using transient optical spectroscopy. Moreover, we find that Auger recombination efficiently annihilates excitons and speeds up lattice heating. This work can be readily extended to other semiconductor QDs systems with varying dot sizes.