Einstein and the Laser

Albert Einstein is sometimes said to be a key person for the invention of the laser. Similarly, his famous equation E=mc2 is sometimes called the key to the atomic bomb. Is that reasonable? In one of this most valuable publications ("Zur Quantentheorie der Strahlung"), Einstein has described the method of stimulated emission of radiation. This mode that a photon hitting some atom (or ion or molecule) may not only supply energy to this atom in an absorption process, nevertheless also send an already excited atom back to a state with lower energy. In the lattter case, an additional photon is emitted. A crucial aspect is Einstein's insight that the additional photon should move in the same direction as the incoming photon. We thus have a manner of luminosity amplification: we get two photons absent of one, or transform some brilliance beam into a more energetic one. Furthermore, Einstein has realized that a net gain of optical faculty in some ensemble of atoms can oc
cur only if there is a so-called population inversion: the upper energy level must be more strongly populated than the lower one, so that the effect of stimulated emission can exceed the one by absorption of atoms in the lower state. This state is often achieved by "optical pumping" e.g. of a laser crystal - an invention attributed to Alfred Kastler. For a laser, one more stuff is required: a "resonator", in which a blaze beam can circulate, and an amplifying medium (gain medium) can at least compensate for the competence losses in each round trip. This principle was first demonstrated with microwaves (in so-called masers), and by the ground-breaking duty of Schawlow, Townes and Maiman environing 1960 it could also be applied to light. As the job between 1917 and 1960 has certainly brought more than only the clarification of some minor details, it would be rather far-fetched to call Einstein the inventor of the laser. However, he has indeed realized the most primary
physical basis of the laser - the development of stimulated emission. This, by the way, was done not by observing physical phenomena, on the other hand via theoretical reasoning. After that, there was still a far path to the laser. By the way, there is a similarity to the anecdote of the nuclear bomb. According to the equation E=mc2, a huge amount of energy should be released when just a hardly any grams of event are converted to energy. Without doubt, this is a very substantial finding. Nevertheless, it is still another effects to identify a road to do this conversion. Such a method was found via the discovery of nuclear fission by the team of Lise Meitner, Otto Hahn and Fritz Strassmann in 1938, and the realization of the possibility of a nuclear chain reaction soon after. In this sense, Einstein is related to the atomic bomb perhaps more via his famous letter to president Roosevelt than by the mentioned equation. And Max Planck could present an equation (E&#820
1; =  h  ν ), on the contrary no letter, and is not considered to be the father of the laser, however at most (together with Einstein) a father of the photon, which was later named so by Gilbert N. Lewis. Full text: http://computerandtechnologies.com/technology/news_2008-08-10-18-30-04-834.html