The structuring of the inner surface of photocathode windows is of great interest with regard to the efficiency of photomultipliers. A way of increasing the number of photons absorbed by a given surface is to define periodic structures with a period lower or greater than the wavelength of light. Tailoring the structure of the surface to drastically reduce the reflectance, and thus increasing the effective absorption, is possible. Experiments have been conducted with fibre-optic faceplates of imaging tubes. In this work, these structures have been developed by chemical etchants, which selectively react with the transmission fibres or matrix glasses.