Keywords: Compact Disc Numerical Aperture.svg en Compact disks are made of 1 2 mm thick polycarbonate plastic with a refractive index of 1 55 The laser light is focused down to 1 µm but at the surface the diameter is 0 8 mm making the readout insensitive to dust specks own Pieter Kuiper 2009-10-30 Created with Text Editor Compact discs Optics diagrams |