Microscopically textured optical storage media

A new optical information storage technique is described which operates by irreversibly altering the absorption properties of a microscopically textured surface. Reflectance changes of greater than a factor of 100 have been obtained by local melting of the surface. A random array of Si columns with cross-sectional dimensions less than 100 nm, formed on a Si film by reactive ion etching, has a visible reflectance of less than 0.01. By irradiation with a focused laser beam, at a power density of ≲8 mW/μm², the columns melt to form a surface with a specular reflectance of ∼0.4. The applicability of this surface structure as a permanent optical storage medium is discussed. In general, this surface texturing can be applied to a wide variety of materials with the advantages of increased sensitivity to the writing beam, large contrast between the written and unwritten areas and reduced lateral energy flow.