Toward Graphene Plasmon-Based Free-Electron IR to X-ray Sources

Rapid progress in nanofabrication methods has fuelled a quest for ultra-compact photonic integrated systems and nanoscale light sources. The prospect of small-footprint, high-quality emitters of short-wavelength radiation is especially exciting due to the importance of extreme ultraviolet and X-ray radiation as research and diagnostic tools in medicine, engineering, and the natural sciences. Here, we propose a highly-directional, tunable, and monochromatic radiation source based on electrons interacting with graphene plasmons (GPs). Our complementary analytical theory and ab-initio simulations demonstrate that the high momentum of the strongly-confined GPs enables the generation of high-frequency radiation from relatively low-energy electrons, bypassing the need for lengthy electron acceleration stages or extreme laser intensities. For instance, highly-directional 20 keV photons could be generated in a table-top design using electrons from conventional radiofrequency (RF) electron guns. The conductive nature and high damage threshold of graphene make it especially suitable for this application. Our electron-plasmon scattering