Frequency-Swept Integrated and Stretched Solid Effect Dynamic Nuclear Polarization

We investigate a new time domain approach to dynamic nuclear polarization (DNP), the frequency-swept integrated solid effect (FS-ISE), utilizing a high power, broadband 94 GHz (3.35 T) pulse EPR spectrometer. The bandwidth of the spectrometer enabled measurement of the DNP Zeeman frequency/field profile that revealed two dominant polarization mechanisms, the expected ISE, and a recently observed mechanism, the stretched solid effect (S 2 E). At 94 GHz, despite the limitations in the microwave chirp pulse length (10 μs) and the repetition rate (2 kHz), we obtained signal enhancements up to ∼70 for the S 2 E and ∼50 for the ISE. The results successfully demonstrate the viability of the FS-ISE and S 2 E DNP at a frequency 10 times higher than previous studies. Our results also suggest that these approaches are candidates for implementation at higher magnetic fields.