Tunable Extremely Ultra-violet Emitter Based on Threshold-less Cherenkov Radiation

Cherenkov radiation (CR), the electromagnetic radiation emitted by a moving charge passing through a dielectric medium, is associated with a velocity above a certain threshold, the radiation power increasing with the particle's velocity, a forward output. To make use of the broadband electromagnetic evanescent <overline>eld surrounding the moving electrons and realize on-chip free electron light source, breaking such high electron energy threshold is a fundamental challenge. This paper reports a new phenomenon of CR in multi-layers hyperbolic metamaterial (HMM) and theoretically demonstrates integrated free electron extremely ultra-violet (UV) light source, where the velocity threshold to generate CR is unexpectedly eliminated. With 0.1keV energy electron, the CR power could be as high as 3x10(11) W/cm(2) in the opposite direction with electron, which verifies the elimination of electron energy to generate CR. The output wavelength covering 80-500nm could be tuning by controlling the applied voltage. This work provides a way to realize threshold-less CR, opens up the possibility of exploring high performance on-chip integrated free electron extremely UV source and optoelectronic devices at different frequency, and offers the platform to study the interaction of flying electrons with artificial nanostructures on chip.