Compact Pulse Slicer for High-Power Submillimeter Waves

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Project Summary / Abstract Complex bio-macromolecules such as membrane proteins play crucial roles in many cellular and physiological processes and specific defects are associated with many known. Determining their three- dimensional structures is one of the main objectives in structural biology and the NIH devotes considerable resources towards this goal. X-ray crystallography and NMR spectroscopy are the major sources for such information. In addition, Electron Paramagnetic Resonance (EPR) spectroscopy, in particular dipolar spectroscopy (PELDOR/DEER/RIDME) is a valuable source for accurate distance information to complement other methods for structure determination. However, NMR suffers from an inherently low sensitivity due to the small nuclear magnetic moment. Long acquisition times are required to achieve sufficient data quality. Combining NMR with Dynamic Nuclear Polarization (DNP) is a great way to overcome this limit, boosting sensitivity and shortening acquisition times by several orders of magnitude. In recent years DNP-enhanced NMR spectroscopy has become an integral part of the NMR spectroscopists toolbox, because the method enables researchers to perform experiments that were previously not possible. While DNP can increase the sensitivity of an NMR experiment drastically, the methodology scales very unfavorably with the magnetic field strength, leading to lower enhancement values at higher magntice fields. This is common to all DNP mechanisms based on continuous wave (cw) radiation of the sample. Pulsed DNP experiments on the other hand do not show this behavior. However, the common approach of creating/shaping pulses at low powers (~ mW) and amplifying them (> 10-100 W) does not work because of the lack of high- power/high-frequency microwave/THz amplifiers. In this SBIR application we propose to develop a compact, turn-key pulse slicer to generate short, high- power pulses from cw sources such as gyrotrons, that are commonly used in DNP-NMR experiments. The system will be easy to operate even for non-microwave engineers and can be readily integrated into existing setups. The successful development of this pulse slicer will bring desperately needed pulse capabilities to systems that otherwise can only be operated in cw mode. This will greatly proliferate the method and is of large interest to many projects funded by the U.S. National Institutes of Health.