Stable ultrafast graphene hot-electron source on optical fiber.

A stable and durable ultrafast electron source is highly desirable for sophisticated vacuum electron technologies. However, free-space excitations based on ultrahigh-power or deep-ultraviolet pulsed lasers usually cause cathode material damage and mechanical vibration even under ultrahigh vacuum. In this work, we present a compact ultrafast electron source consisting of graphene integrated on an optical fiber, taking advantage of the ultrafast hot-electron emission from graphene and well-defined single-mode excitation from the optical fiber. With mild excitation (~1 GW/cm², infrared laser), an ultrashort electron pulse (width of ~ 80 fs) with high stability (fluctuation ≤±0.5% in 8 hours) and longevity (T₉₀ > 500 hours) can be generated even under relatively high ambient pressure (up to 100 Pa). This compact source has been facilely integrated into a commercial electron microscope for time-resolved imaging and spectroscopy. Our graphene optical fiber-based ultrafast electron source offers a promising solution to support the development of vacuum electron instruments.