Ronald R. Willey, Willey Optical, Consultants, Melbourne, FL
A new three-layer, with three materials, antireflection (AR) coating design has been discovered. The designs for the classic three- and four-layer AR coatings in common use, when optimized with respect to the photopic response of the eye, can reduce the luminous (Y) value of reflectance to between 0.05 and 0.08 or 0.05% to 0.08%, as compared to 4.3% for uncoated crown glass. This invention can further reduce this to 0.02%. The classical three-layer AR design employs successive layers on the glass substrate of: medium, high, and low indices of refraction which are approximately one quarter, one half, and one quarter wavelength of optical thickness at a wavelength near the center of the visible spectrum. This discovery uses a notably different material for the second layer, and thereby reduces the photopic reflectance by a factor of 2 to 4 times. The performance depends a great deal on the detail index of refraction properties of this material.