395 GHz Sample Holder Waveguide for Dynamic Nuclear Polarization*

A major issue in nuclear magnetic resonance (NMR) is the low sensitivity which can be achieved as a result of the small magnetic moment in nuclei. At the MagLab, we exploit dynamic nuclear polarization (DNP), which increases NMR sensitivity through a process in which electron spins transfer their larger polarization to the nuclei of interest, to yield larger DNP signals at 14 T. For DNP experiments, our spectrometer uses a sample holder which doubles as a waveguide for the microwave used to saturate the electrons in the sample under study. The lack of axial symmetry in this sample holder limits our range of experiments.

To overcome this limitation, we are manufacturing axially symmetric sample holder-waveguides by coating sample tubes with a conductive silver layer. The layer must have thickness and conductivity such that it is transparent to a 600 MHz radio frequency, yet reflective to a 395 GHz microwave. Our process consists of creating silver layer prototypes using various deposition methods, characterizing the prototypes, replicating an optimized prototype on our sample tubes, and implementing the final product in DNP experiments.