Patent ID: 6501598
Filing Date: 2002-12-31
Classification: G02B

Abstract:
A prism, comprising:a base member having first and second faces intersecting with each other, said base member including calcium fluoride; a first antireflection film formed on the first face of said base member; and a second antireflection film formed on the second face of said base member, each of said first and second antireflection films having a high-refractive-index layer with a relatively high refractive index and a low-refractive-index layer with a relatively low refractive index, said high refractive-index layer including thorium fluoride, and said low-refractive-index layer including aluminum fluoride, wherein each of said first and second antireflection films includes alternately layered said high-refractive-index layer and said low-refractive-index layer, and said first antireflection film includes an even number of layers, said high-refractive-index layer is arranged immediately on the first face of said base member, and said low-refractive-index layer is arranged at an outermost surface of said first antireflection film.