Effective Hamiltonian based DNP Sequence Optimization

TL;DR

This paper uses continuous Floquet theory to optimize pulsed DNP sequences, significantly improving their bandwidth and power efficiency for enhanced NMR signal strength at low temperatures.

Contribution

It introduces a novel application of effective Hamiltonians derived from Floquet theory to optimize pulsed DNP sequences, enabling better control and efficiency.

Findings

On-resonance sequence achieves 100 MHz bandwidth.

Off-resonance sequence covers 20 MHz at 50 MHz offset.

Optimized sequences operate effectively with 25-20 MHz microwave power.

Abstract

Dynamic nuclear polarization (DNP) enhances the intensity of NMR signals by transferring polarization from electron spins to nuclei via microwave irradiation. Pulsed DNP methods offer more control on the spin dynamics than conventional continuous-wave approaches. Here, we report on-resonance and off-resonance DNP sequences optimized using effective Hamiltonians derived from continuous Floquet theory. Experiments at 80 K and 0.35 T using a sample of 5 mM Trityl OX063 in a glycerol-d8/D2O/H2O matrix (60:30:10, v/v/v) demonstrate that the optimized on-resonance sequence achieves 100 MHz electron offset bandwidth, while the offresonance sequence cantered at an electron offset of 50 MHz can cover 20 MHz, with 25 MHz and 20 MHz of microwave power, respectively. These results demonstrate that continuous Floquet theory is a useful framework for the optimization of pulsed DNP sequences.