|Abstract:The improved transmission and mirror system for a 263 GHz DNP-NMR spectrometer has been designed and numerically simulated based on the geometric optics theory and the vector diffraction theory. The system includes two corrugated waveguides, a parabolic mirror and an angle-adjustable phase-correcting mirror. The simulation results show that a well-focused Gaussian-like output beam with 96.43% scalar Gaussian mode content, 92.33% vector Gaussian mode content has been obtained. The direction of the output beam can be changed by only adjusting the angle of the phase-correcting mirror to match the DNP-NMR sample. The scalar Gaussian mode content is about 96%, and the vector Gaussian mode content is about 92% when the direction of the output beam changes within ± 15o.