By now, optical storage media, like CD, DVD, Bluray and HD-DVD have prevailed in all areas. Compared with magnetic media they had and have a very high storage density. All optical storage media are based on the same technical principle. Like a record, there are depressions (pits) and flat bodies (lands), metallized in plasma processes. Using a laser and a photo detector, the pits and lands are illuminated and their reflection is read out.