These are the lasers inside compact disc players, laser printers, supermarket scanners, and fiber-optic cables used in telephone lines. Most of the time, these technologies use tiny semiconductor lasers. Telephone companies convert sound to electrical pulses, then convert the pulses to laser light that can travel through fiber-optic cables. This is more efficient than traditional phone technology, which sends calls over copper wires. With a laser that pulses very quickly, one glass fiber the width of a human hair can transmit the calls of more than 20,000 wires.
Lasers can also record and reproduce music on compact discs.
The sound is recorded by a laser beam that burns a pattern of dots into a disc. A tiny semiconductor laser in a compact disc player reads the dots and converts them back to sound. Since only light touches the disc, a CD player gives very clean, clear sound, without the background noise from scratches and dust that you hear on records. Compact discs are quickly replacing other kinds of recordings, and not just for home stereos. Libraries use them to store data bases, encyclopedias, and other information to access by computer.