Microwave frequency modulation in continuous-wave far-infrared ESR utilizing a quasioptical reflection bridge

TL;DR

This paper introduces a novel frequency-modulation method for electron spin resonance measurements in the 210-420 GHz range, utilizing a high-frequency ESR spectrometer without resonant microwave components to improve performance.

Contribution

The study presents a new FM technique for high-frequency ESR that avoids nonlinear microwave issues, enabling effective measurements up to 420 GHz.

Findings

Successful ESR spectra acquisition at 210, 315, and 420 GHz.

Verification of sensitivity through conduction electron spin resonance in KC$_{60}$.

FM achieved via modulation of a 13 GHz oscillator and frequency multiplication.

Abstract

We report the development of the frequency-modulation (FM) method for measuring electron spin resonance (ESR) absorption in the 210-420 GHz frequency range. We demonstrate that using a high-frequency ESR spectrometer without resonating microwave components enables us to overcome technical difficulties associated with the FM method due to nonlinear microwave-elements, without sacrificing spectrometer performance. FM was achieved by modulating the reference oscillator of a 13 GHz Phase Locked Dielectric Resonator Oscillator, and amplifying and frequency-multiplying the resulting millimeter-wave radiation up to 210, 315 and 420 GHz. ESR spectra were obtained in reflection mode by a lock-in detection at the fundamental modulation frequency, and also at the second and third harmonic. Sensitivity of the setup was verified by conduction electron spin resonance measurement in KC$_{60}$.