How CD-Recordable and CD-Rewritable Dyes Work

The cyanine & phthalocyanine dyes used in CD-Recordable discs are photosensitive organic compounds, similar to that used in making photographs (which explains why companies like Kodak and Fuji are in this business.) When a CD-R is recorded the dye is heated by the writing laser and becomes opaque (or absorbtive) through a chemical reaction to the heat (and possibly to some mingling with nearby semi-melted polycarbonate according to some sources), so it's not likely that any process will be developed to reverse the process and make previously burned CD-Rs reusable.

CD-Rewritable (which hasn't been released yet) uses a different kind of data-bearing layer from that in ordinary CD-Recordable, one which uses a phase change process to alter its state from a reflective state to a light absorbing state rather than an irreversable chemical change as in cyanine-based CD-R. This phase change CAN be reversed to make the area erasable and reusable.

The phase change technology used in CD-Rewritable does not incorporate any magnetic field like those in Magneto Optical disks. Rather, it alters the state of the recording layer from crystaline to non-crystaline, (and vise versa) so that the cystaline portion can allow the metalized layer to reflect the laser better while the non-crystaline portion absorbs the laser beam, so it is not reflected. As in pressed CDs and CD-Recordables, these alternating binary states create the data-bearing signal.

In order to achieve these effects in the recording layer, the CD-Rewritable recorder use three different laser powers:

1. The highest laser power, which is called "Write Power," creates a non-crystaline (absorbtive) state on the recording layer.

2. The middle power, also known as "Erase Power," melts the recording layer and converts it to a reflective crystaline state.

3. The lowest power, which is "Read Power", does not alter the state of the recording layer, so it can be used for reading the data.

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