3D printed alumina as a millimeter-wave optical element

We present transmission and loss measurements of 3D printed alumina and reflectance measurement of a sample with 3D printed sub-wavelength structures anti-reflection coatings (SWS-ARC). For a band between 160 and 700 GHz we find an index of refraction n = 3.11 ± 0.01 and loss tan δ = 0.002 ± 0.003. Transmission measurements between 160 and 250 GHz of a sample with SWS-ARC 3D printed on one side give a reduction of reflectance from a maximum of 64% to a maximum of 31% over the band, closely matching predictions. These first measurements of the index and loss over this frequency band suggest that the material could be useful for astrophysical applications.