Interference effects in super-radiant THz sources

摘要

A new class of linear accelerator (linac) based THz facilities, aiming to provide peak THz fields in the GV/ m regime from highly charged, ultra-short relativistic electron bunches is currently studied and developed worldwide. These facilities are based on low emittance, electron beams delivered by a linear radio frequency (RF) driven accelerator followed by one or several magnetic chicanes that act as bunch compressor. THz radiation is then emitted coherently for wavelengths appropriately longer than the longitudinal electron bunch length upon one single pass through any of the typical sources of synchrotron radiation. This allows for an enormous flexibility in the generated spectral, spatial and temporal properties of the THz pulses. Together with the theoretically large scalability and simplicity of these sources, they are discussed as extension of the THz pulses from laser-based THz sources towards extreme transient THz fields and high repetition rates with more than 10 projects currently being pursued worldwide. In this respect it is timely to investigate if current idealized theoretical descriptions can be technically fully realized. As our contribution to this effort, in this paper it is shown by numerical and analytical calculations that the interference effects between different THz radiators, intrinsically emitting in the forward direction of a linac can crucially affect radiation properties.