Designing Broadband Pulsed Dynamic Nuclear Polarization Sequences in Static Solids

International audienceDynamic nuclear polarization (DNP) is an NMR hyperpolarization technique that mediates polarization transfer from unpaired electrons with large thermal polarization to NMR-active nuclei via microwave (mw) irradiation. The ability to generate arbitrarily shaped mw pulses using arbitrary waveform generators opens up the opportunity to remarkably improve the robustness and versatility of DNP, in many ways resembling the early stages of pulsed NMR. We present here novel design principles based on single-spin vector effective Hamiltonian theory to develop new broadband DNP pulse sequences, namely an adiabatic version of XiX-DNP and a Broadband Excitation by Amplitude Modulation (BEAM)-DNP experiment. We demonstrate that the adiabatic BEAM-DNP pulse sequence may achieve a 1 H enhancement factor of ∼ 360, which is better than ramped-amplitude NOVEL at ∼ 0.35 T and 80 K in static solids doped with trityl radicals. Additionally, the bandwidth of the BEAM-DNP experiments is about 3 times the 1 H Larmor frequency (∼50 MHz). The generality of our theoretical approach will make the design principles outlined here helpful in the development of new pulsed DNP sequences