Maser
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A maser is any optical amplifier that produces coherent microwaves due to stimulated emission. The term comes from the acronym microwave amplification by stimulated emission of radiation. Masers led to the invention of optical lasers, and now that materials have been made to lase across a wide spectrum of electromagnetic radiation, masers are often referred to as microwave lasers.
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History
Theoretically, 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 microwaves at a frequency of 24 gigahertz. For their research in this field Townes, Basov and Prokhorov were awarded the Nobel Prize in Physics in 1964.
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.
Uses
Masers serve as high precision frequency references, as, for example in an atomic clock. They are also used as electronic amplifiers in radio telescopes. For more information about frequency reference masers, see atomic clock.
Another example is given by telescopic masers, which may use arrays of chromium atoms in an insulating aluminium oxide crystal as amplifiers, pumping the energy in at a different radio frequency. That is, they use polished strips of synthetic ruby. As the input signal comes in, a gold comb (made of gold because it is slow to corrode and change shape) distributes it along the strip of polished ruby. As the radio wave moves through the crystal, it knocks electrons into different atomic orbitals. As the electrons move to their new lower energy orbits, they add to the wave that knocked them down, leading to a population inversion. The comb-fingers are spaced so that the desired radio waves add together as they move down the crystal. This means that unwanted radio waves don't add together, and are therefore filtered out, leading to a highly coherent induced emission.
Masers are also currently being studied by the United States Military as a form of vehicle-mounted riot control device. A maser can be used to heat up water molecules in the skin, producing a burning sensation without causing permanent damage, unless concentrated on a target for an extended period of time.
Technology
There are a number of types of masers. Generally one can break these down into type as the gas masers, solid masers, and as yet only hypothesized liquid masers. In each of these categories there are many different subtypes; for example, solid state masers may be divided into two level solid state masers,' three level cavity masers
In operation, some masers use liquid helium for cooling to temperatures around 4 kelvin. This reduces the noise from vibrating electrons, nuclei, and other charged particles.
Masers in Nature
Masers also occur 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.
Masers in Science Fiction
Masers are the most recognizable weapon in the Godzilla movie monster series as well as Toho's other monster movies. Maser tanks are often deployed against monsters. The maser tank fires a bolt of electricity, presumably created by amplified microwaves. Like in most science fiction, the science behind the maser tank is dubious and not supported by real world physics.
External links
- Noble gas Maser (http://cfa-www.harvard.edu/Walsworth/Activities/DNGM/old-DNGM.html)
- Marine Corps Times — 'The People Zapper' (http://www.globalsecurity.org/org/news/2001/010227zapper.htm)
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References
J.R. Singer, Masers, John Whiley and Sons Inc., (1959)