Maser
Maser, acronym for microwave
amplification by stimulated emission of radiation, a device that amplifies or
generates microwaves or radio waves. A maser producing radiation in the optical
region is called a laser.
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PRINCIPLE OF OPERATION
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As in lasers, amplification
of radiation in masers is obtained by stimulated emission. This occurs when a
photon induces an excited atom or molecule to fall to a lower energy state
while emitting a photon of the same frequency as the incoming photon. The
emitted photon travels in the same direction and in phase with the incoming
photon, which is not absorbed during the interaction. The amplitudes of the two
waves add up, and amplification of the incoming wave has taken place. Masers
make use of those transitions in molecules or crystals that correspond to the
energies of microwave or radio frequencies.
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TYPES OF MASERS
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Charles Townes
American physicist Charles Townes won
the 1964 Nobel Prize in physics. He made fundamental contributions in quantum
theory and significantly improved radar technology.
The first maser oscillator
was developed by the American physicists Charles Hard Townes (1915- ),
James P. Gordon, and Herbert J. Zeiger in 1954, and made use of the frequency
of the ammonia molecule. This frequency corresponds to the energy of the photon
emitted when the nitrogen atom moves from one side to the other of the triangle
formed by the three hydrogen atoms in an ammonia molecule. The hydrogen maser
makes use of the frequency corresponding to that of the photon released when
the spin of the proton in a hydrogen atom flips over with respect to the spin
of the atom's electron. Paramagnetic masers use energy transitions
corresponding to the orientations of the magnetic moments of paramagnetic ions
in crystalline substances placed in an external magnetic field. Different
frequencies can be obtained by varying the magnetic field, thus allowing the
tuning of a paramagnetic maser from less than a megacycle to several hundreds
of megacycles.
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APPLICATIONS
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Because of the high stability
of the generated frequencies, masers serve as time standards in atomic clocks.
Masers are also used as low-noise radio frequency amplifiers in satellite
communication and radio astronomy.
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