Comparison between Single-mode Treatment and Multi-mode Treatment of a Coaxial Bragg Resonator for a Terahertz Cyclotron Autoresonance Maser Oscillator

As a coaxial Bragg structure has more complex geometry configuration than a cylindrical or a planar Bragg structure, for simplicity of calculation a single-mode treatment is often adopted. However, heterogeneity of a coaxial Bragg structure always gives rise to the multi-mode conversion, which can change the performance of the resonator. Based on the scattering matrix method, detailed comparison between the single-mode treatment and the multi-mode treatment is presented to a coaxial Bragg resonator for a cyclotron autoresonance maser (CARM) oscillator operating in the higher-order mode TE₆₁ at frequency of 0.35 THz. Results indicate that there is a little difference between the results obtained by these two treatments to the upstream reflector due to its shallow ripple amplitude, whereas to the downstream reflector, due to its relatively deep ripple amplitude, an apparent difference occurs at the operating frequency and consequently it gives notable difference to the frequency response and Q-factor of the whole resonator. Optimization shows possible application of a coaxial Bragg resonator with a single higher-order mode operation in constructing a terahertz CARM oscillator.