Multiharmonic electron paramagnetic resonance for extended samples with both narrow and broad lines

Area of Science:

• Electron Paramagnetic Resonance (EPR) Spectroscopy
• Magnetic Resonance Imaging
• Spectroscopic Techniques

Background:

• Conventional EPR spectroscopy is limited by spectral distortion and line broadening at higher modulation amplitudes.
• Optimizing modulation amplitude is crucial for balancing signal-to-noise ratio and spectral resolution.
• Narrow spectral lines are particularly susceptible to distortion with increased modulation.

Purpose of the Study:

• To demonstrate multiharmonic electron paramagnetic resonance (EPR) spectroscopy for improved spectral analysis.
• To evaluate the effectiveness of multiharmonic reconstruction with varying modulation amplitudes.
• To assess the impact on signal-to-noise ratio and spectral linewidths.

Main Methods:

• Utilized a rapid scan coil driver and Litz wire coils to generate modulation amplitudes up to 17 G at 41 kHz.
• Acquired 2-D data using Xepr software on a Bruker E500T, digitized with a Bruker SpecJet II.
• Calculated signals at modulation frequency and harmonics via digital phase-sensitive detection.

Main Results:

• The number of detectable harmonics increased with the modulation amplitude to linewidth ratio.
• Multiharmonic reconstruction yielded spectra with only ~10% broadening, even at modulation amplitudes five times the narrowest linewidth.
• Signal-to-noise ratio improved with modulation amplitude up to the linewidth of the narrowest features.

Conclusions:

• Multiharmonic EPR reconstruction effectively minimizes spectral distortion caused by high modulation amplitudes.
• This method significantly improves signal-to-noise ratios without compromising spectral resolution for narrow lines.
• The multiharmonic approach decouples the optimal modulation amplitude from the narrowest spectral linewidth, offering greater experimental flexibility.