High-field and high-frequency EPR

This introductory essay surveys the motivation for high-field/high-frequency electron paramagnetic resonance (HFEPR), and identifies some of the technology needed to further develop HFEPR. For many spin systems HFEPR increases resolution of the EPR spectra, makes the spectra more nearly first-order, thus simplifying interpretation, and/or changes the motional regime or relaxation times that dominate important features of the spectra. In other cases, spectra can only be seen at high field. Applications of HFEPR range over most problems that involve unpaired electrons in materials sciences, chemistry, physics, and biology. Applications of HFEPR will be enhanced by improvements in resonators, lower-noise sources and detectors, and fast switches for pulse experiments.