The demonstration of a working ruby laser by Theodore Maiman at Hughes Aircraft Corporation (see Maiman, 1960) was the culmination of over a decade of research in the stimulation of radiation, which began early in this century. In 1916, Albert Einstein laid the foundation for the invention of the laser and its predecessor, the maser, in a proof of Planck's law of radiation.1 In 1900 the German physicist Max Planck had proposed a formula relating atoms to the spontaneous emission of electromagnetic energy. Einstein sought to relate Planck's proof to his own theories of quantum mechanics; he suggested that photon emission could be stimulated, not just spontaneously produced (see the technical appendix for a detailed explanation of laser theory). Einstein's proposal was ignored, however, until after World War II.

During World War II, several laboratories were established to develop radar. The most prominent laboratories were the Massachusetts Institute of Technology (MIT) Radiation Laboratory and the Columbia University Radiation Laboratory in the physics department. These research sites were enormously successful, and in 1946 the Joint Services Electronics Program (JSEP) was established to continue laboratory funding in peacetime. The main recipients of JSEP funds were MIT and Columbia University, and JSEP founded laboratories at Harvard in 1946 and Stanford in 1947. A variety of military projects were funded at these laboratories; one of the beneficiaries of JSEP was Charles Townes of Columbia University.

Townes had worked on radar bombing systems at Bell Laboratories in New Jersey during World War II and was a founding father of molecular and millimeter-wave spectroscopy. He became deeply involved in spectroscopy after the war, and military experts thought his work could be used in radar. Prior research of the electromagnetic spectrum had been sequential; the longest waves (electric current) were studied first, followed by shorter radio waves and then microwaves. It seemed logical to physicists to continue this pattern of development, so many projects sought to conquer waves of millimeter length. Waves with a higher frequency would be more compact than radar waves and had the potential to provide greater secrecy in communication. In 1950, the U.S. Office of Naval Research asked Townes to organize the Advisory Committee on Millimeter Wave Generation. The following year, while in Washington, D.C., to attend this committee meeting, Townes was inspired with an idea while sitting on a park bench. He thought that an oscillator made with deuterated ammonia (ND3) might cause the emission and amplification of microwaves (10-3 to 1 meter wavelengths).2


Albert Einstein, Mitt. Phys. Ges., 16(18):47, Zurich, 1916. An English translation is in B. L. van der Waerden, ed., Sources of Quantum Mechanics. Amsterdam: North-Holland, 1967.


This idea clearly had its roots in Einstein's theory that electromagnetic emissions could be stimulated.

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