Terahertz passive components for Dynamic Nuclear Polarization Nuclear Magnetic Resonance applications

Terahertz radiation, THz = 1012 Hz, refers to electromagnetic signals with frequencies in the range of 0.3 to 3 THz, and wavelengths between 1 and 0.1 mm. This part of the electromagnetic spectrum is located in between millimeter waves at lower frequencies, and far-infrared at higher frequencies. THz is one of the last underemployed portions of the electromagnetic spectrum, despite the interest it raises for research and applications. One application that makes use of THz signals is Dynamic Nuclear Polarization - Nuclear Magnetic Resonance (DNP-NMR). It allows for a dramatic increase in signal sensitivity over conventional NMR. The latter is a widespread technique used from Chemistry to Material Science. First commercial DNP-NMR spectrometers appeared on the market in 2008. However, the application can still benefit from developments in its THz components. This thesis reports on the development of THz wave guiding-components for DNP-NMR. In particular, Corrugated wave-guiding components are studied, in view of their low propagation losses. A new manufacturing technique for those Corrugated wave-guiding components is presented: the Stacked Rings technology. This technology circumvents the limitations in achievable mechanical precisions with conventional machining, and allows for the scaling of Corrugated wave-guiding components through the THz spectrum. Corrugated waveguides made by Stacked Rings are presented at 263 GHz, and are successfully integrated in commercial DNP-NMR spectrometers. A transmission line made by Stacked Rings at 140 GHz for a Dissolution DNP pre-polarizer is also presented. The pre-polarizer uses DNP to generate contrast agents for Magnetic Resonance Imaging. An increase in the pre-polarizer’s DNP performances is demonstrated. Finally, the Stacked Rings technology is used to demonstrate the performances of a modular set of Corrugated wave-guiding components between 500 and 750 GHz for test and measurement applications. All components are characterized at THz frequencies with two experimental platforms and associated methodologies developed in the framework of this thesis. A crucial THz component for DNP-NMR applications is the probe. It couples the THz signal to the sample under study, while also integrating features necessary for NMR. A chapter of this thesis reports on an experimental and simulation study of the THz field distributions in this complex environment with dimensions larger than the THz wavelength. Probe chambers of commercial DNP-NMR probes are studied, complex field distributions are put into evidence, and key parameters influencing these field distributions are identified for future optimizations.