Understanding Lasers

Chapter 9.13.1: Optical Disk Lasers

9.13.1 Optical Disk Lasers

The first CD players reached the market in 1980, and since then they have become ubiquitous and inexpensive. They incorporate a single GaAlAs laser emitting at 780 nm, packaged in a playback head that includes focusing optics and a light detector, which moves back and forth radially over the spinning disk. The original CD format was read-only, but writeable disks were added later. Writing requires more power than reading, and is not offered in the least expensive players.

DVD players and drives use 650-nm lasers, which can be focused to smaller spot sizes than 780-nm lasers. Smaller spot size and tightening other tolerances allow DVDs to squeeze in about six times more data than CDs. As in CD drives, the laser is packaged in an optical head for reading, and for writing if that option is included.

The emerging generation of HD optical disks uses 405-nm blue diode lasers, but so far the volume is small. The design approach is similar to that in other optical disk players.

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