Foundations
In 1917 Albert Einstein, in his paper Zur Quantentheorie der Strahlung (On the Quantum Theory of Radiation), laid the foundation for the invention of the laser and its predecessor, the maser, in a ground-breaking rederivation of Max Planck's law of radiation based on the concepts of probability coefficients (later to be termed 'Einstein coefficients') for the absorption, spontaneous emission, and stimulated emission of electromagnetic radiation.
In 1928, Rudolf W. Ladenburg confirmed the existence of stimulated emission and negative absorption.[5] In 1939, Valentin A. Fabrikant predicted the use of stimulated emission to amplify "short" waves.[6]
In 1947, Willis E. Lamb and R. C. Retherford found apparent stimulated emission in hydrogen spectra and made the first demonstration of stimulated emission.[7]
In 1950, Alfred Kastler (Nobel Prize for Physics 1966) proposed the method of optical pumping, which was experimentally confirmed by Brossel, Kastler and Winter two years later.[8]
The first working laser was demonstrated on 16 May 1960 by Theodore Maiman at Hughes Research Laboratories.[9] Since then, lasers have become a multi-billion dollar industry. By far the largest single application of lasers is in optical storage devices such as compact disc and DVD players,[citation needed] in which a semiconductor laser less than a millimeter wide scans the surface of the disc. The second-largest application is fiber-optic communication. Other common applications of lasers are bar code readers, laser printers and laser pointers.
Maser
Main article: Maser
In 1953, Charles H. Townes and graduate students James P. Gordon and Herbert J. Zeiger produced the first microwave amplifier, a device operating on similar principles to the laser, but amplifying microwave rather than infrared or visible radiation. Townes's maser was incapable of continuous output. Nikolay Basov and Aleksandr Prokhorov of the Soviet Union worked independently on the quantum oscillator and solved the problem of continuous output systems by using more than two energy levels and produced the first maser. These systems could release stimulated emission without falling to the ground state, thus maintaining a population inversion. In 1955 Prokhorov and Basov suggested an optical pumping of multilevel system as a method for obtaining the population inversion, which later became one of the main methods of laser pumping.
Townes reports that he encountered opposition from a number of eminent colleagues who thought the maser was theoretically impossible—including Niels Bohr, John von Neumann, Isidor Rabi, Polykarp Kusch, and Llewellyn H. Thomas[1].
Townes, Basov, and Prokhorov shared the Nobel Prize in Physics in 1964 "For fundamental work in the field of quantum electronics, which has led to the construction of oscillators and amplifiers based on the maser-laser principle."