In pulsed dynamic nuclear polarization (DNP), electron polarization is transferred to nuclei by means of a microwave pulse sequence. With the help of spin dynamics and optimal control, the polarization transfer can be fully optimized. The eventual goal is to improve the sensitivity of high-resolution magic-angle spinning (MAS) NMR beyond what is currently possible with continuous-wave DNP methods like the solid-effect and the cross-effect.
For the time being, pulsed DNP experiments are only possible at low magnetic fields. The basic reason is that suitable microwave sources are not available above roughly 95 GHz. Nevertheless, in recent years considerable progress has been made in the development of DNP pulse sequences. Beyond the original NOVEL sequence,[1] there now exists a family of DNP sequences, which appear, based on their matching condition, compatible with high-field MAS DNP.[2-5]
The theoretical description of the transfer of polarization by periodic DNP pulse sequences in a dipolar-coupled electron-nuclear spin system is under control. Numerical simulations of this process are a useful tool to investigate the efficiency of pulsed DNP conditions, but do not correctly predict all experimental observations. Moreover, the ultimate DNP pulse sequence has not yet been found. In my talk I will update you on the latest developments and insights.