Bragg resonator cavity for time-resolved microwave conductivity measurement

Time-resolved microwave conductivity (TRMC) is a well-established technique for characterizing charge carriers in materials. This technique relies on a sensitive resonant microwave cavity to detect small changes in the material’s conductivity induced by a laser pulse. Conventional TRMC systems typically employ iris-coupled resonant cavities. In this work, we present a systematic theoretical, numerical, and experimental study aimed at integrating a Bragg-resonator-based cavity into TRMC measurements. First, we optimize the multilayer structure, composed of silica glass and air, inside the rectangular waveguide operating in the Ka-band, in order to bring the bandgap into our operating frequency range. Next, we introduce a defect into the structure, which induces resonance within the bandgap. At the resonance frequency, the electric field is strongly confined within the defect region, creating a highly sensitive area for TRMC measurements. Then, the position of a substrate containing a thin film is optimized by calculating the sensitivity factor both theoretically and numerically. The experimental characterization of the proposed cavity presents a good convenient with theoretical and simulation result. Finally, TRMC measurements were carried out using the Bragg resonator cavity, and a clear signal attributed to charge excitation was obtained. This opens new perspectives for the use of Bragg cavities in TRMC, by taking advantage of their strong field confinement.