Dispersion electron spin resonance with the loop-gap resonator

The loop-gap resonator, a novel microwave lumped-circuit structure, when used as a sample resonator in electron-spin-resonance spectroscopy, permits the direct detection of dispersion signals with greatly decreased demodulation of the FM noise that originates in the microwave oscillator. The improvement arises from two factors: 65 times higher energy density for a given input power and 12 times lower resonator Q compared with a typical cavity resonator. The signal-to-noise ratio for the dispersion signal of DPPH is predicted to be improved by a factor of 12×65=780; experimentally a factor of 700 was realized.