Design and Measurement of Possible Wide-band 67-116 GHz ALMA Vacuum Window Anti-reflection Layers

A new broad-band vacuum lens/window design is required for the new Atacama Large Millimeter/submillimeter Array (ALMA) band 2 receiver, intended to cover 67-116 GHz. A suitable anti-reflection coating (ARC) for this will be necessary. This paper presents the optimization of a candidate ARC design in ultra-high molecular weight polyethylene (UHMWPE), as well as simulations and measurements of candidate designs in silicon. Machined triangular grooves are used as the ARC for the UHMWPE candidates, and stacked cuboids for the silicon candidate design.