Abstract
This paper studies various mechanisms to enhance the coherent Smith-Purcell radiation (SPR) at terahertz frequencies using particle-in-cell (PIC) simulations. A simple analytical dispersion relation is derived to predict the frequency of the evanescent surface wave of the open grating, which is excited by a backward-wave oscillation mechanism and emits radiation at harmonics of this frequency, and the cavity mode frequencies of the Orotron-like device, all in excellent agreement with the simulation data. The grating parameters are optimized to minimize the starting current of a continuous electron beam for exciting coherent SPR. It is demonstrated that a prebunched beam can be used to selectively excite coherent SPR at desired SPR angle and frequencies that are higher harmonics of the beam bunching frequency, where the starting current requirement is eliminated. Our PIC simulations show the dynamics of modes development and competition for the Orotron-like open cavity structure, which owns a lower starting current than the surface mode process. This oscillation mode dominates at steady state and enhances the radiated power by more than 2 orders of magnitude.
Highlights
Development of compact, tunable and high-power terahertz (THz) sources has been drawing continuous interest in recent years [1,2,3]
A simple analytical dispersion relation is derived to predict the frequency of the evanescent surface wave of the open grating, which is excited by a backward-wave oscillation mechanism and emits radiation at harmonics of this frequency, and the cavity mode frequencies of the Orotron-like device, all in excellent agreement with the simulation data
Equation (2) is derived by assuming that the electromagnetic fields inside the grooves may be approximated by a TEM mode [10,44], which are matched to the Floquet fields outside the grating, which behave like e−γny=Leiðpnx=L−ωtÞ
Summary
Development of compact, tunable and high-power terahertz (THz) sources has been drawing continuous interest in recent years [1,2,3]. A simple analytical dispersion relation is derived for the open grating Smith-Purcell structure, which accurately predicts the operating frequency of the (evanescent surface mode) backward wave oscillation and the consequent coherent (superradiant) harmonic SPR. In the open grating surface-wave-excited SPR device of Dartmouth College, the continuous electron beam is bunched at the evanescent frequency, which varies as the grating parameters changes, even for fixed beam energy and grating period [26], and limits the performance of such a device. Accurate analytical dispersion is derived to determine the oscillation condition for both the surface wave of the open grating and the cavity mode of the Orotron-like device, following which the simulation results are presented.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Physical Review Special Topics - Accelerators and Beams
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
