Maser | Research & Encyclopedia Articles

Maser

Although the knowledge and use of lasers is now widespread, the laser is actually a light-emitting cousin to the maser, a device used to generate and amplify radio and light waves. The maser--an acronym for Microwave Amplification by the Stimulated Emission of Radiation --was originally designed to meet the need for an oscillator that could produce radiation shorter than one millimeter in wavelength. Previously, scientists had used microwave oscillators to study the basic structure of matter (the branch of physics known as microwave spectroscopy), but by the late 1940s it became increasingly clear that coherent oscillators at shorter wavelengths were essential.

Two concepts figured highly into the development of the maser: coherence and stimulated emission. Coherence describes a wave or particle whose vibratory pattern is "in step," the crests and troughs aligned perfectly. Stimulated emission was first studied by Albert Einstein (1879-1955) in relation to his theory of relativity; it claimed that a group of excited atoms could be stimulated so as to emit their radiation in a controlled manner. Although these two theories laid the groundwork for maser research, actual development could not begin until after World War II. During the war, tremendous advances were achieved in radar technology, and it was these advances that truly opened scientists' minds to the concept of masers.

Maser research was introduced independently by Nikolai Gennadievich Basov and Alexander Mikhailovich Prokhorov in the Soviet Union, and by Charles Hard Townes and his students at Columbia University in the United States. The first working maser was built by Townes and his associates in 1954 using ammonia gas (NH₃). A beam of excited ammonia molecules was sent through a cylindrical "focuser" which allowed only those molecules in the high-energy state to pass through. This new high-energy beam was guided into a resonant cavity where, under the influence of an electrical field, amplification by stimulated emission of radiation was achieved, producing a microwave output corresponding to the resonance frequency of ammonia. In 1956, Townes and his colleagues at the University of Paris showed that maser action was possible in certain solids, leading to the development of the more common ruby maser, and the first operating "optical maser," or laser (Light Amplification by the Stimulated Emission of Radiation), was built in 1960. For their efforts in this field, Townes, Basov and Prokhorov shared the 1964 Nobel Prize for physics.

The decade following 1954 saw tremendous advancement upon Townes' original ammonia-based model. One by-product was the atomic clock, a device whose extreme accuracy relied upon the undeviating regularity with which molecules vibrate. Ruby masers were used in radio astronomy to amplify very weak radiation from distant radio sources such as stars and planetary probes, sources that were previously undetectable among the din of background noise. Optical masers, or lasers, have found countless applications in numerous fields including medicine, engineering, and communications.