394. How does laser surgery work?
Lasers are used in medicine in a variety of ways. In surgery, lasers are used mostly as intense sources of heat. They deposit large amounts of power into small areas, vaporizing and "cooking" tissue. Because they produce very local heating, there is no much bleeding from a cut made with a laser scalpel. In some eye surgery, intense pulsed lasers are used and take advantage of the peculiar effects that happen at very high intensities. The most important of these effects is the creation of free charged particles, which reflect and absorb the laser beam. Because it creates free charged particles when it encounters a surface, an intense pulsed laser beam only penetrates a few microns into a surface. The charged particles that it creates prevent it from traveling deeper, even in a clear material. In eyes, that allows surgeons to remove outer layers of tissue without damaging inner layers or the retina beyond.