Laser devices use light to store, transfer, or print images and text; they are also used in a wide range of other applications, including surgery and weaponry. The coherent radiation of the laser gives it special strength. The laser (Light Amplification by Stimulated Emission of Radiation) started life as an extension of the maser, or "Microwave Amplification by Stimulated Emission of Radiation." As its name indicates, the maser is an amplifier that was originally used for amplifying weak radio signals from space. Light waves are very much like radio waves but with a much shorter wavelength.

The laser generates light energy by converting the energy states of a material. The energy level of an atom is a function of its temperature. Its lowest energy level is called its "ground state." The application of additional heat, light, or electric field can raise its energy level. The familiar...