Electron sources represent an enabling technology for all cutting-edge applications of electron accelerators, two of the most notable ones being the X-ray free electron laser (FEL) and the electron microscope. FELs were enabled by the development of high-brightness electron sources, and they have changed the paradigm for a broad spectrum of scientific research. Electron microscopes have achieved sub-Å spatial resolution through the introduction of a cold field-emitter and aberration correction optics. Development of ultrashort high-brightness electron beam made it feasible to explore relativistic electrons for Ultrafast Electron diffraction (MeV-UED) [1]. Recent development in MeV-UED [2-3] has enabled broad scientific opportunities in ultrafast material science and chemical dynamics, such as revealing the energy flow in superconductor [4] and atomic movie of light-induced structural distortion in the perovskites solar cell [5]. Single-shot MeV-UED was successfully employed for the first observation of heterogeneous melting [6]. In the gas phase UED, we have successfully made transition from proof-of-principle experiments to investigating the unknown dynamics in chemical interesting systems, such as making a real space movie of a nuclear wavepacket passing through conical intersections [7].

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Science enabled by the high-brightness Electron Beams

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