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A maser is a device that produces s. See the section on terminology below for more on this. HISTORY Theoretically, reflecting principles previously discussed by Joseph Weber at the June 1952 conference of the Institute Of Radio Engineers 1, the principle of the maser was described by Nikolay Basov and Alexander Prokhorov from Lebedev Institute Of Physics at an ''All-Union Conference on Radio-Spectroscopy'' held by USSR Academy Of Sciences in May 1952 . They subsequently published their results in October 1954 . Independently, Charles H. Townes , J. P. Gordon , and H. J. Zeiger built the first maser at Columbia University in 1953 . The device used Stimulated Emission in a stream of energised Ammonia molecules to produce amplification of Microwave s at a frequency of 24 Gigahertz . Townes later worked with Arthur L. Schawlow to describe the principle of the ''optical maser'', or ''laser'', which Theodore H. Maiman first demonstrated in 1960 . For their research in this field Townes, Basov and Prokhorov were awarded the Nobel Prize In Physics in 1964 . TECHNOLOGY The maser is based on the principle of Stimulated Emission proposed by Albert Einstein in 1917. When atoms have been put into an excited energy state, they can amplify radiation at the proper frequency. By putting such an amplifying medium in a Resonant Cavity , feedback is created that can produce Coherent Radiation . Some common types of masers Atomic beam masers
Gas masers
Solid State masers
The dual . USES Masers serve as high precision Frequency references. These "atomic frequency standards" are one form of Atomic Clock . They are also used as Electronic Amplifier s in Radio Telescopes . Hydrogen maser Today, the most important type of maser is the Hydrogen Maser which is currently used as an Atomic Frequency Standard . Together with other types of atomic clocks, they constitute the " Temps Atomic International " or TAI. This is the international time scale, which is coordinated by the Bureau International Des Poids Et Mesures , or BIPM. It was Norman Ramsey and his colleagues who first realized this device. Today's masers are identical to the original design. The maser oscillation relies on stimulated emission between two Hyperfine levels of atomic Hydrogen . Here is a brief description of how it works:
ASTROPHYSICAL MASERS See Also: Astrophysical maser Stimulated microwave and radio wave emission is observed in Astronomy , and this is usually called "masing", even in the absence of the resonant feedback that would be required for a true maser. Technically this form of stimulated emission is called Superradiant Emission , and it is closely associated with lasing and masing. Such emission is observed from Water (H2O), Hydroxyl Radicals ( OH ), Methanol (CH3OH), Formaldehyde (CH2O), and Silicon Monoxide (SiO). Maser-like stimulated emission also occurs in nature in Interstellar Space . Water molecules in Star -forming regions can undergo a Population Inversion and emit radiation at 22 GHz, creating the brightest Spectral Line in the Radio universe. Some water masers also emit radiation from a Vibrational Mode at 96 GHz. TERMINOLOGY The meaning of the term ''maser'' has changed slightly since its introduction. Initially the acronym was universally given as "microwave '''a'''mplification by '''s'''timulated '''e'''mission of '''r'''adiation," which described devices which emitted in the , where the base element of a kinetic system is a Molecule , even if it happens to be Monatomic . This should not be confused with the usage of the term in the molecular sciences, where it refers to a Bound State comprising two or more atoms. Initially, visible light oscillators based on stimulated emission were called ''optical masers'', but this terminology has become uncommon. It is more conventional now to refer to devices that emit in the X-ray through Infrared portions of the spectrum as Laser s, and devices that emit in the microwave region and below as ''masers''. There is some debate over whether ''maser'' or ''laser'' is the correct generic term for all devices that produce coherent electromagnetic waves through stimulated emission. Distinct names were originally proposed for devices that emit in each portion of the spectrum, including ''grasers'' ( Gamma Ray lasers), ''xasers'' ( X-ray lasers), ''uvasers'' ( Ultraviolet lasers), '' lasers'' ( Visible lasers), ''irasers'' ( Infrared lasers), ''masers'' ( Microwave masers), and ''rasers'' ( RF masers). Most of these terms never caught on, however, and all have now become obsolete except for ''maser'' and ''laser''. MASERS IN SCIENCE FICTION Masers often appear as weapons in Science Fiction movies and novels. Their characteristics often differ from those of real masers, however, and it is doubtful whether a practical maser weapon such as these can actually be made. Some notable science fiction appearances of masers:
SEE ALSO FOOTNOTES REFERENCES
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