Harmonics generation of a terahertz wakefield free-electron laser from a dielectric loaded waveguide excited by a direct current electron beam

Tunable Cherenkov radiation based on a van der Waals semiconductor α-MoO3 and graphene hybrid

In this Letter, we explore the Cherenkov radiation properties of α-phase molybdenum trioxide (α-MoO₃). We demonstrate that the asymmetric, forward, and reverse Cherenkov radiation can simultaneously exist by rotating the α-MoO₃ slab at the same working frequency and structure. In addition, thanks to the tunable functionalities of graphene, the conversion of forward and reverse Cherenkov radiation can be actualized by altering the Fermi level of graphene. These dynamically adjustable features provide a novel, to the best of our knowledge, and intuitive way for tunable Cherenkov radiation in the mid-infrared range, which opens up new opportunities in designing and manufacturing tunable radiation sources in future.

Intrinsically reducing divergence angle of Cherenkov radiation from dielectric capillary

Narrow-band terahertz (THz) Cherenkov radiation can be excited as a relativistic electron bunch passes through the dielectric capillary with sub-millimeter radius. However, due to the diffraction effect, the radiation will enter free space with a large divergence angle, which makes it difficult to collect the radiation energy efficiently. In this Letter, to deal with this challenge, we propose to add a new dielectric layer, which satisfies a special relationship with the electron velocity, between the metal coating and original dielectric layer in the capillary. According to numerical simulation and theoretical analysis results, the divergence angle of radiation is significantly suppressed, and the peak power density is also enhanced by over two orders. As a result, the transmission efficiency from the radiation source to the optical system can be increased to over 90%. We expect that this method will provide a new way to generate THz Cherenkov radiation.