Quasi-monochromatic THz pulse generation using Cherenkov radiation from a spatially modulated electron beam

Cherenkov radiation forms a wave front in a direction that depends on the density of the medium and the velocity of charged particles; therefore, ordinary electron bunches do not generate coherent radiation unless they are sufficiently compressed. In this work, we present the generation of a quasi-monochromatic THz pulse using an electron bunch with a periodic structure generated from a small rf gun. A coherent THz pulse was generated by matching the tilt angle of the electron bunch and Cherenkov radiation angle with a rf deflector. Furthermore, we attempted to render the THz pulse quasi-monochromatic by adding a periodic structure to the electron bunch using a multi-slit. Finally, using several band-pass filters, we successfully confirmed that the quasi-monochromatic operation was performed at frequencies of 0.2 and 0.3 THz.