Observation of narrow-band Si L-edge Čerenkov radiation generated by 5 MeV electrons

Narrow-band Čerenkov radiation at 99.7 eV has been generated by 5 MeV electrons in a silicon foil, with a yield ~1×10 ^-3 photon/electron. These measurements demonstrate the feasibility of a compact, narrow-band, and intense soft x-ray source based on small electron accelerators. The observed yield and dependence of the photon spectrum on emission angle are in agreement with theoretical predictions for Čerenkov radiation based on refractive index data of silicon.