The development of the Excimer laser is the key element that has made laser eye surgery possible. Created by IBM, Excimer lasers (the name is derived from the terms excited and dimers) use reactive gases, such as chlorine and fluorine, mixed with inert gases such as argon, krypton or xenon. When electrically stimulated, a pseudo molecule (dimer) is produced that, when lased, produces light in the ultraviolet range. (See How Lasers Work for detailed information about lasers.)
The Excimer laser is a cool laser, which means that it does not heat up the surrounding air or surfaces. Instead, a very tightly-focused beam of ultraviolet light is emitted. The ultraviolet light is absorbed by the upper layer of the surface that it contacts. The sheer amount of ultraviolet light is too much for most organic materials (such as the cornea of the eye) to absorb, resulting in the breakdown of the molecular bonds of the material.
The ultraviolet beam of light only penetrates a microscopic amount, less than a nanometer (a billionth of a meter), into the surface of the cornea. The heat created from the energy released by the laser is dissipated along with this microscopic layer of the cornea. This process is known as photoablation.
The Excimer laser is incredibly precise. It has the ability to focus a beam as small as 0.25 microns. Considering that a typical human hair is 50 microns in diameter, that means that the Excimer laser is capable of removing 0.5 percent of a human hair's width at a time!
The operation of the Excimer laser is a complicated and delicate process. In fact, a dedicated technician is used just to set up and operate the machine in conjunction with the ophthalmologist performing the surgery.