A laser is a chamber containing a solid, liquid or gas that gives the laser its wavelength, or color. Lasers work best when they're zapping something of an opposite color-a ruby laser's red light will burn away a green tattoo, for example. At either end of this chamber you have a mirror. When the machine is turned on, electricity stimulates the particles inside the chamber and emits photons, or light particles. These particles bounce around between the mirrors, gaining intensity, until it forms a strong beam.
Pulses deliver less energy and less heat collects at the receiving end.
The most popular is the CO2 laser. It emits a powerful infrared beam that can cut and vaporize tissue. This laser is used in gynecology, dermatology and plastic surgery because a minimum of tissue is destroyed. Argon lasers fire a blue-green beam that is absorbed by blood and pigment. They're used to coagulate blood cells and vaporize tattoos.