Mechanical anti-reflection Structure for optical devices in the mm band

A major challenge in the implementation of optical element in the millimetre band is to minimize the radiation loss caused by reflection. The widely used method is based on the realization of an Anti-Reflection Coating (ARC), which exploits the behaviour of interference the radiation generated by the deposition of one or more layers of polymeric material on the optical element, so as to obtain a unique surface having refractive index conveniently selected. The major limitations that affect the ARC, reside in the complexity of manufacturing, with consequent increase of costs, and possible bonding process issues after several cooling cycles; an essential feature to achieve measurements at these wavelengths. Here we report about an alternative and innovative technique based on the realization of a mechanical Anti-Reflection Structures (ARS), possibly a more simple and economic manufacture, based on the mechanical processing of the surface of a dielectric material. The antireflective behaviour is linked to the geometrical textureof the surface. The simulations of these ARS provide us a detailed analysis of the optical properties for dierent geometrical realizations. The results will be compared with those of the ARC and further experimentally validated. Particular attention is put on to the analysis of the possible presence of spurious polarization effects, because this type of technology could find employment in the realization of cold optical elements for telescopes devoted CMB observations.