Because of the special properties of laser light, many new and revolutionary applications have become possible in areas of communications, medicine, measurement, holography, energy generation, entertainment, and sadly, warfare. In communication, diode lasers are used to inject light into optical fibers, which act like wires, carrying the light signal to the fiber's other end. Here the signal is received and decoded. These fibers can be 20 miles long. With such systems, telephone companies can simultaneously transmit millions of telephone calls along a single fiber the diameter of a human hair, a huge savings over an equivalent copper-wire system.
Doctors now use lasers in a variety of applications.
In particularly bloody operations, the laser can be used as a scalpel with the distinct advantage of cauterizing the incision as it's made. The laser-knife is also perfectly sterile because the only thing touching the patient is light. Tattoos and other specific types of skin markings can be removed with a laser. Using pulsed lasers, an eye surgeon can spot-weld a detached retina to its proper place on the back of the eye without any cutting or discomfort to the patient. By routing the powerful laser light down a fiber, a cardiologist will someday remove the plaque from the inside of arteries, reducing clogging that can lead to heart attacks and strokes.