Optical Chopper for Longitudinal-Detected Electron Paramagnetic Resonance at 188 GHz/6.7 T

Area of Science:

• Magnetic Resonance Spectroscopy
• Physical Chemistry
• Materials Science

Background:

• Dynamic nuclear polarization (DNP) enhances nuclear magnetic resonance (NMR) sensitivity by transferring polarization from electrons to nuclei.
• Optimizing DNP polarizing agents requires understanding their structure, electron paramagnetic resonance (EPR) line widths, and relaxation properties.
• Current EPR characterizations often occur under conditions different from DNP experiments, limiting agent design.

Purpose of the Study:

• To demonstrate a low-cost, home-built setup for in situ EPR detection within a dual resonance DNP-NMR/EPR probe.
• To enable EPR characterization under experimental conditions relevant to DNP.
• To facilitate the design of more efficient DNP polarizing agents.

Main Methods:

• Utilized an optical chopper to modulate microwave irradiation, inducing modulation in electron spin longitudinal magnetization (Mz).
• Implemented a LOngitudinal-Detected (LOD) EPR spectroscopy technique.
• Performed measurements using a dual resonance DNP-NMR/EPR probe at 6.7 T/188 GHz.

Main Results:

• Successfully demonstrated in situ EPR detection using an optical chopper.
• Acquired EPR spectra for TEMPOL that agreed well with those obtained via electrical modulation.
• Validated the proof-of-principle for an optical chopper EPR spectrometer integrated with DNP.

Conclusions:

• The developed setup provides a cost-effective method for in situ EPR characterization during DNP.
• This approach allows for EPR measurements under DNP-relevant conditions, aiding in polarizing agent optimization.
• The optical chopper method offers a viable alternative for EPR detection in DNP-NMR systems.