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

Area of Science:

• Physics
• Spectroscopy
• Materials Science

Background:

• High-frequency electron spin resonance (ESR) spectroscopy presents unique technical challenges.
• Traditional methods often struggle with nonlinear microwave components at these frequencies.

Purpose of the Study:

• To develop and validate a frequency-modulation (FM) method for ESR absorption measurements in the 210–420 GHz range.
• To overcome limitations of nonlinear microwave elements in high-frequency ESR spectrometers.

Main Methods:

• Implemented FM by modulating a 13 GHz Phase-Locked Dielectric Resonator Oscillator.
• Amplified and frequency-multiplied millimeter-wave radiation to 210, 315, and 420 GHz.
• Utilized lock-in detection in reflection mode at fundamental and harmonic frequencies.

Main Results:

• Successfully measured ESR absorption spectra in the millimeter-wave range.
• Demonstrated overcoming technical difficulties without sacrificing spectrometer performance.
• Verified setup sensitivity using conduction electron spin resonance in KC60.

Conclusions:

• The developed FM method is effective for high-frequency ESR measurements.
• The approach enables sensitive ESR spectroscopy without problematic resonating microwave components.
• This advancement facilitates detailed studies of electron spin dynamics at high frequencies.