Bridged loop–gap resonator: A resonant structure for pulsed ESR transparent to high-frequency radiation

Abstract

A new and inexpensive X-band resonator structure for pulsed electron-spin resonance and electron-nuclear-double-resonance applications is introduced. The resonator consists of a bridged loop structure and is distinguished by a good reproducibility and reliability. It has a high filling factor and an adjustable Q value and is transparent to radio frequency fields with an upper limit >100 MHz. The inner diameter of 5 mm allows convenient sample access of standard 4-mm quartz tubes in the temperature range between 4 and 300 K. Numerical computations of the resonant frequencies, the Q values, and the three-dimensional distributions of the electromagnetic fields are presented. They are based on a discretization method for the solution of Maxwell’s equations and include all dielectric elements of the resonator structure. The field homogeneity in the sample area and the influence of the dimensions and the thickness of the metallic layers on field intensity, quality factor, and resonant frequency are determined experimentally. The performance of the resonator is demonstrated by a novel field-swept echo-induced electron-spin-resonance experiment with jumping magnetic field vectors.