Broadband Enhancement of Cherenkov Radiation Using Dispersionless Plasmons

As one of leading technologies in detecting relativistic particles, Cherenkov radiation plays an essential role in modern high‐energy and particle physics. However, the limited photon yield in transparent dielectrics makes efficient Cherenkov radiation only possible with high‐energy particles (at least several MeV). This restriction hinders applications of Cherenkov radiation in free‐electron light source, bio‐imaging, medical therapy, etc. Broadband enhancement of Cherenkov radiation is highly desired for all these applications, but still widely acknowledged as a scientific challenge. To this end, a general approach is reported to enhance the photon yield of Cherenkov radiation using dispersionless plasmons. Broadband dispersionless plasmons can be realized by exploiting either the acoustic nature of terahertz plasmons in a graphene‐based heterostructure or the nonlocal property of optical plasmons in a metallodielectric structure. When coupled to moving electrons, such dispersionless plasmons give rise to a radiation enhancement rate more than two orders of magnitude (as compared with conventional Cherenkov radiation) over an ultrabroad frequency band. Moreover, since the phase velocity of dispersionless plasmons can be made as small as the Fermi velocity, giant radiation enhancements can be readily induced by ultralow‐energy free electrons (e.g., with a kinetic energy down to 3 eV), without resorting to relativistic particles.