Broadband Terahertz Generation in a Corrugated Waveguide with matched Phase and Group Velocities

Siaber, Sergey and Gratus, Jonathan and Seviour, Rebecca and Jamison, Steven and Boyd, Taylor (2023) Broadband Terahertz Generation in a Corrugated Waveguide with matched Phase and Group Velocities. arxiv.org.

Abstract

We show that it is possible to design corrugated waveguides where phase and group velocities coincide at an inflection point of the dispersion relation, allowing an extended regime of interaction with a charge particle beam. This provides a basis for designing travelling slow-wave structures with a broadband interaction between relativistic charged particle beams and propagating terahertz waves allowing an energy exchange between beam and wave, amplifying terahertz radiation. We employ Fourier-Mathieu expansion, which gives approximate analytic solutions to Maxwell equations in a corrugated waveguide with periodically undulating cross-section. Being analytic, this enables quick design of corrugated waveguides, determined from desirable dispersion relations. We design a three dimensional waveguide with the desired dispersion and confirm the analytical predictions of the wave profile, using numerical simulations. Madey's theorem is used to analyse the strength of the wave-beam interaction, showing that there is a broad frequency interaction region.