3D Printed Alumina as a Millimeter-Wave Optical Element

Abstract

We present millimeter and sub-millimeter room temperature transmission and loss measurements of 3D printed alumina disc and of a disc with one-sided 3D printed sub-wavelength structures anti-reflection coatings (SWS-ARC). For four bands spanning 158 - 700~GHz we find an index of refraction consistent with $n=3.107\pm 0.007$. The loss over the entire frequency band between 158~GHz and 700~GHz spans $1\cdot 10^{-3}\le \tan \hat{I}´\le 2.49\cdot 10^{-3}$ with 10%-30% uncertainty at the lower range of frequencies shrinking to $\sim 2\%$ at the higher frequencies. As expected, constructive and destructive interference fringes that are apparent with the flat disc data are absent with the disc that has SWS-ARC. The measured data are consistent with finite element analysis predictions that are based on the measured shape of the SWS. At frequencies between 158~GHz and 200~GHz, below the onset of diffraction effects, reflectance is reduced from a maximum of 64% to about 25%, closely matching predictions. These measurements of the index, loss, and SWS-ARC of 3D printed alumina suggest that the material and fabrication technique could be useful for astrophysical applications.

Accepted for Publication in JATIS-250148. 11 Pages, 5 Figures, 2 Tables