Textured surfaces: Optical storage and other applications

Textured surfaces consisting of submicron columns or cones have been formed in a variety of surfaces using reactive ion etching. On metals, insulators, and semiconductors this texturing forms a graded index matching layer which reduces reflection of visible light to as low as 0.1%. The optical properties can be permanently altered on a ∠l μm size scale by irradiation with a low power laser beam and this has been explored as a new optical storage medium. The light energy transforms the optically absorbing textured surface to a nonabsorbing smooth one by melting. Reflectance changes of greater than a factor of 100 have been demonstrated at ∠10 mW light power. The textured surfaces have also been used with dielectric materials to create high transparency optical elements. Highly absorbing films of Ge and Si, that were earlier studied as solar photothermal absorbers, have been investigated as optical storage media. The production, morphology and optical properties of these surfaces are described.