CD-R (recordable, writable CD)
A write-once CD consists of four layers:
- Polycarbonate substrate layer
- Information carrier consisting of an organic dye layer made of cyanine (bluish) or phthalocyanine dyes (greenish)
- reflective gold or silver coating
- Acrylic varnish protective layer
In contrast to the "normal" CD, the CD-R does not have a pit structure but the as yet unwritten data track ("groove" or "pregroove") is a simple groove that is embedded in the substrate layer. This serves as an "address" for finding the recorded information again. The recorder determines the number of revolutions of the disc from the frequency.
When "burning", the dye layer is heated to 250 ° C by a laser beam and inflated in the process. When reading out, light can no longer be reflected from the rear metal layer at these points and thus signals a pit.