Laser stands for Light Amplification by the Stimulated Emission of Radiation. Lasers work by producing an intense beam of bright light that travels in one direction. The laser has the unique ability to produce one specific color or wavelength of light, which can be varied in its intensity and pulse duration. The newest laser systems have become remarkably precise and selective, allowing treatment results and safety levels not previously available. All lasers contain an energized substance that can increase the intensity of light that passes through it. This substance is called the amplifying medium and it can be a solid, a liquid or a gas.
             Einstein can be considered as the father of the laser. 80 years ago he postulated photons and stimulated emission and won the Nobel Prize for related research on the photoelectric effect. This section discusses the historical evolution from microwave lasers to optical lasers and finally to x-ray lasers and lasers discovered in space. Some theorists were on the right track, especially Planck, who proposed that nature acted by using "quanta" of energy. But it was the young, unknown Albert Einstein who explained everything and started the field of quantum mechanics with his paper on the photoelectric effect. Einstein showed that light does not consist of continuous waves, nor of small, hard particles. Instead, it exists as bundles of wave energy called photons. Each photon has an energy that corresponds to the frequency of the waves in the bundle. The higher the frequency (the bluer the color), the greater the energy carried by that bundle.
             Einstein's Nobel Prize was not awarded for either one of his relativity theories - the Nobel Committee thought them too speculative at the time. Rather Einstein won the prize for explaining the photoelectric effect. Two of Einstein's 1905 papers were on the theory of atoms and molecules, yet there were still many scientists in 1905 who did not believe in atoms ...