Maser

Source: Wikipedia, the free encyclopedia.
For other uses, see Maser (disambiguation).
The first prototype ammonia maser in front of its inventor Charles H. Townes. The ammonia nozzle is at left in the box, the four brass rods at center are the quadrupole state selector, and the resonant cavity is at right. The 24 GHz microwaves exit through the vertical waveguide Townes is adjusting. At bottom are the vacuum pumps.
A hydrogen radio frequency discharge, the first element inside a hydrogen maser (see description below)

A maser is a device that produces

spacecraft communication
ground stations.

Modern masers can be designed to generate electromagnetic waves at microwave

frequencies and radio and infrared frequencies. For this reason, Townes suggested replacing "microwave" with "molecular" as the first word in the acronym "maser".[1]

The laser works by the same principle as the maser, but produces higher frequency coherent radiation at visible wavelengths. The maser was the precursor to the laser, inspiring theoretical work by Townes and Arthur Leonard Schawlow that led to the invention of the laser in 1960 by Theodore Maiman. When the coherent optical oscillator was first imagined in 1957, it was originally called the "optical maser". This was ultimately changed to laser, for "light amplification by stimulated emission of radiation". Gordon Gould is credited with creating this acronym in 1957.

History

The theoretical principles governing the operation of a maser were first described by

USSR Academy of Sciences
in May 1952, published in October 1954.

Independently,

Theodore H. Maiman
created the first working model in 1960.

For their research in the field of stimulated emission, Townes, Basov and Prokhorov were awarded the Nobel Prize in Physics in 1964.[6]

Technology

The maser is based on the principle of stimulated emission proposed by Albert Einstein in 1917. When atoms have been induced into an excited energy state, they can amplify radiation at a frequency particular to the element or molecule used as the masing medium (similar to what occurs in the lasing medium in a laser).

By putting such an amplifying medium in a

resonant cavity, feedback is created that can produce coherent radiation
.

Some common types

21st-century developments

In 2012, a research team from the

p-Terphenyl as the amplifier medium.[8][9][10]
It produced pulses of maser emission lasting for a few hundred microseconds.

In 2018, a research team from Imperial College London and University College London demonstrated continuous-wave maser oscillation using synthetic diamonds containing nitrogen-vacancy defects.[11][12]

Uses

Masers serve as high precision

FETs.[13]

During the early 1960s, the

S-band microwave signals received from deep space probes.[14] This maser used deeply refrigerated helium to chill the amplifier down to a temperature of 4 kelvin. Amplification was achieved by exciting a ruby comb with a 12.0 gigahertz klystron
. In the early years, it took days to chill and remove the impurities from the hydrogen lines.

Refrigeration was a two-stage process, with a large Linde unit on the ground, and a crosshead compressor within the antenna. The final injection was at 21 MPa (3,000 psi) through a 150 μm (0.006 in) micrometer-adjustable entry to the chamber. The whole system

milliwatt
 (dBm).

Hydrogen maser

Main article: Hydrogen maser
A hydrogen maser.

The hydrogen maser is used as an

Norman Ramsey and his colleagues first conceived of the maser as a timing standard. More recent masers are practically identical to their original design. Maser oscillations rely on the stimulated emission between two hyperfine energy levels of atomic hydrogen
.

Here is a brief description of how they work:

Astrophysical masers

Main article: Astrophysical maser

Maser-like stimulated emission has also been observed in nature from

GHz, creating the brightest spectral line in the radio universe. Some water masers also emit radiation from a rotational transition at a frequency of 96 GHz.[17][18]

Extremely powerful masers, associated with

active galactic nuclei, are known as megamasers
and are up to a million times more powerful than stellar masers.

Terminology

The meaning of the term maser has changed slightly since its introduction. Initially the acronym was universally given as "microwave amplification by stimulated emission of radiation", which described devices which emitted in the microwave region of the electromagnetic spectrum.

The principle and concept of stimulated emission has since been extended to more devices and frequencies. Thus, the original acronym is sometimes modified, as suggested by Charles H. Townes,[1] to "molecular amplification by stimulated emission of radiation." Some have asserted that Townes's efforts to extend the acronym in this way were primarily motivated by the desire to increase the importance of his invention, and his reputation in the scientific community.[19]

When the laser was developed, Townes and

Schawlow and their colleagues at Bell Labs pushed the use of the term optical maser, but this was largely abandoned in favor of laser, coined by their rival Gordon Gould.[20] In modern usage, devices that emit in the X-ray through infrared portions of the spectrum are typically called lasers
, and devices that emit in the microwave region and below are commonly called masers, regardless of whether they emit microwaves or other frequencies.

Gould originally proposed distinct names for devices that emit in each portion of the spectrum, including grasers (

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 (apart from in science fiction) obsolete except for maser and laser.[citation needed
]

See also

References

  1. ^ a b Townes, Charles H. (1964-12-11). "Production of coherent radiation by atoms and molecules - Nobel Lecture" (PDF). The Nobel Prize. p. 63. Archived (pdf) from the original on 2020-08-27. Retrieved 2020-08-27. We called this general type of system the maser, an acronym for microwave amplification by stimulated emission of radiation. The idea has been successfully extended to such a variety of devices and frequencies that it is probably well to generalize the name - perhaps to mean molecular amplification by stimulated emission of radiation.
  2. ^ American Institute of Physics Oral History Interview with Weber
  3. ISBN 978-1420033403
    .
  4. doi:10.1103/PhysRev.99.1264
    .
  5. doi:10.1103/PhysRev.112.1940
    .
  6. ^ "The Nobel Prize in Physics 1964". NobelPrize.org. Retrieved 2020-08-27.
  7. ^ The Dual Noble Gas Maser, Harvard University, Department of Physics
  8. S2CID 124247048
    .
  9. ^ Palmer, Jason (16 August 2012). "'Maser' source of microwave beams comes out of the cold". BBC News. Archived from the original on July 29, 2016. Retrieved 23 August 2012.
  10. ^ Microwave Laser Fulfills 60 Years of Promise
  11. PMID 29565370
    .
  12. ^ Scientists use diamond in world's first continuous room-temperature solid-state maser, phys.org
  13. ^ "Low Noise Amplifiers – Pushing the limits of low noise". National Radio Astronomy Observatory (NRAO).
  14. ^ Macgregor S. Reid, ed. (2008). "Low-Noise Systems in the Deep Space Network" (PDF). JPL.
  15. ^ "Time and Frequency From A to Z: H". NIST. 12 May 2010.
  16. S2CID 26146516
    .
  17. Bibcode:1991ASPC...16..163N
    .
  18. hdl:10831/91303
    .
  19. ISBN 978-0-684-83515-0
    .
  20. ISBN 978-0-684-83515-0
    .

Further reading

  • J.R. Singer, Masers, John Whiley and Sons Inc., 1959.
  • J. Vanier, C. Audoin, The Quantum Physics of Atomic Frequency Standards, Adam Hilger, Bristol, 1989.

External links

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