Patent ID: 9069126
Filing Date: 2015-06-30
Classification: G02B

Abstract:
1. An optical element comprising a substrate that is transparent to light having a used wavelength region and an antireflection coating formed on the substrate, wherein the antireflection coating includes an intermediate layer formed on the substrate, and an undulation layer that is formed on the intermediate layer and has a plurality of convexes arrayed with spacing shorter than a shortest wavelength in the used wavelength region, wherein the undulation layer has a portion where refractive index increases from a light incident side to the substrate, wherein the intermediate layer has a first layer closest to the substrate, and a second layer formed on the first layer, and wherein when a refractive index of the first layer to light having a wavelength of 550 nm is denoted by n1, a refractive index of the second layer to the light having the wavelength of 550 nm is denoted by n2, and a refractive index of the substrate to the light having the wavelength of 550 nm is denoted by ns, the following conditional equations are satisfied: