Charles H. Townes of coherent radiation, for which he invented the acronym "maser" (for Microwave Amplification by Stimulated Emission of Radiation). When the same principle was applied to higher frequencies, the term "laser" was used (the word "light" substituting for the word "microwave"). During 1953, Townes, James P. Gordon, and H. J. Zeiger built the first ammonia maser at Columbia University. This device used stimulated emission in a stream of energized ammonia molecules to produce amplification of microwaves at a frequency of about 24.0 gigahertz. From 1959 to 1961, he was on leave of absence from Columbia University to serve as Vice President
Sound amplification by stimulated emission of radiation one quantum well to another neighbouring well it produces a phonon. External energy pumping (e.g. a light beam or voltage) can help to the excitation of an electron. Relaxation of an electron from one of the upper states may occur by emission of either a photon or a phonon. This is determined by the density of states of phonons and photons. Density of states is the number of states per volume unit in an interval of energy (E, E+dE) that are available to be occupied by electrons. Both phonons and photons are bosons and thus, they obey Bose–Einstein statistics. This