THz-range free-electron laser ESR spectroscopy: techniques and applications in high magnetic fields

TL;DR

This paper demonstrates the use of picosecond-pulse free-electron-laser radiation for continuous-wave THz-range ESR spectroscopy, enabling high-resolution multi-frequency measurements in high magnetic fields with applications to various materials.

Contribution

It introduces a novel combination of linac-based FELs with pulsed magnetic fields for advanced THz ESR spectroscopy, achieving broad frequency coverage and high spectral resolution.

Findings

Successful implementation of FEL-based ESR spectroscopy in the THz range.

Achieved spectral resolution better than 1%.

Demonstrated spectra in DPPH and organic materials.

Abstract

The successful use of picosecond-pulse free-electron-laser (FEL) radiation for the continuous-wave THz-range electron spin resonance (ESR) spectroscopy has been demonstrated. The combination of two linac-based FELs (covering the wavelength range of 4 - 250 $\mu$m) with pulsed magnetic fields up to 70 T allows for multi-frequency ESR spectroscopy in a frequency range of 1.2 - 75 THz with a spectral resolution better than 1%. The performance of the spectrometer is illustrated with ESR spectra obtained in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and the low-dimensional organic material (C$_6$H$_9$N$_2$)CuCl$_3$.