Instrumentation for high sensitivity, high power, millimetre wave, electron paramagnetic resonance

Pulsed Electron Paramagnetic Resonance (EPR) is now a standard magnetic resonance characterisation technique used in the analysis of paramagnetic defects, transition metal complexes and organic radicals in materials and biomolecular systems. Pulsed EPR is now commonly used to measure distances between spin labels or transition metals in proteins, RNA and DNA, to evaluate structure, conformational changes and binding. Most EPR measurements have traditionally been undertaken at frequencies of 10 GHz at fields of 0.34 T. However, recently we have shown that there are substantial advantages to moving to higher fields of 3.4 T and measuring at 94 GHz at power levels of 1 kW. Sensitivity can improve by orders of magnitude - and substantial gains can be made in time resolution. Such systems require flexible, and precise timing control of coherent mm-wave pulses at kW power levels, and delivery of those pulses to samples at cryogenic samples, followed by coherent detection of signals at sub-nW power levels with low deadtime. In this paper we briefly outline the major applications, technical requirements and opportunities for mm-wave EPR, before briefly outlining the critical mm-wave components in a low deadtime, mm-wave EPR system that currently operates with state-of-the-art performance.