Пардон, по собственному недосмотру потерял начало раздела.

3.3 Metal (Reflective) Layer

The metal layer in optical discs reflects the laser beam back to the la- ser photosensor in the laser head. Three types of reflective metals are typically used for this layer: aluminum, gold, and silver or silver al- loy. In “double-layer” DVDs, silicon is sometimes used as one of the semireflective layers.

3.3.1 Metal Layer in RW, ROM, and RAM Discs

RW, ROM, and RAM discs (CD-RW, CD-ROM, DVD-RW, DVD+RW, DVD-ROM, DVD-RAM) use aluminum for the reflective layer, main- ly because it is inexpensive and easy to apply. Aluminum oxidizes on exposure to oxygen from the environment or to moisture that has penetrated the disc. In some earlier CDs, poor sealing allowed oxygen to come into contact with the aluminum metal layer, causing the aluminum to oxidize. Oxidation of the aluminum diminishes its reflectivity, making the disc unreadable by the laser, and is some- times referred to as disc “rot.” It is the primary cause of ROM disc degradation from environmental influences. Not so, however, for RW and RAM disc degradation; the phase-changing film in these discs normally degrades at a faster rate than the aluminum in the disc oxidizes.