Abstract: A product capable of extremely high absorption of electromagnetic radiation, including visible light, useful in optical applications and as a decorative panel comprises a body made of anodizable metal, preferably aluminum having a roughened surface over which an oxide layer is deposited by anodization. The anodized surface is characterized by a roughened surface of pronounced peaks and valleys and a columnar, fault-ridden structure of the anodized oxide layer itself.The product is made by honing the anodizable metal surface by impacting it with aluminum oxide particles, preferably of 100 to 200 mesh size, to form peaks and valleys thereon. After honing, the surface is anodized under controlled conditions to develop the oxide layer thereover. After anodizing, the surface may be dyed and sealed. A vacuum drying and hydrogen fluoride treatment step to dry and "water-proof" the surface may be utilized to eliminate reflectance peak values at certain wavelengths.

Abstract: In an interferometer a beam-splitter reflector such as a compound prism is provided having an interface and a base normal thereto. An entrance face and exit face are aligned with respect to the interface to provide a zero order interface fringe along an axis of one face when a reflecting surface such as an autocollimating mirror is parallel to the base. Also, the zero order interference fringe is fixed at the apex of the prism and rotates as a function of angular misalignment of the reflecting surface with respect to a plane parallel to the prism base. Position of the fringe is measured to provide a high resolution indicaton of angular misalignment of the reflecting surface.