Work Package 2 - Technology Advancements

Non-Adiabatic Rapid Scan (NARS) was introduced as a method to obtain pure-absorption EPR spectra while maintaining the thermal equilibrium condition of continuous-wave EPR. Using modern digital detection, the traditional lock-in amplifier is replaced by digital filtering. For the same collection time, NARS spectroscopy has a factor of 2 in SNR compared to optimally chosen field modulation. For a spectra with disparate linewidths or narrow hyperfine features, the SNR increase is more.

Due to the relatively large 3 dB bandwidth (33 MHz) of the micro-helix, combining NARS with arbitrary-waveform generator (AWG) frequency sweeps allows for a 1 mT equivalent sweep. Additional signal averaging occurs when field steps are used and spectra are collapsed together. Segmented NARS has an added benefit of removing low frequency baseline.

Frequency sweep has a number of advantages compared to field sweep modulation:

  • No eddy-current forces are present on the resonator, lowering potential noise.
  • Background of frequency sweep is not field dependant and may average out with field step averaging.
  • Speed of the frequency sweep can be significantly faster than that of field modulation, allowing for passage or Rapid Scan EPR techniques with systems that have short T2.
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