Product Code Database
A maser is a device that produces coherent electromagnetic waves (microwaves), through amplification by stimulated emission. The term is an acronym for microwave amplification by stimulated emission of radiation. Nikolay Basov, Alexander Prokhorov and Joseph Weber introduced the concept of the maser in 1952, and Charles H. Townes, James P. Gordon, and Herbert J. Zeiger built the first maser at Columbia University in 1953. Townes, Basov and Prokhorov won the 1964 Nobel Prize in Physics for theoretical work leading to the maser. Masers are used as timekeeping devices in , and as extremely low-noise microwave amplifiers in and deep-space spacecraft communication ground-stations.
Modern masers can be designed to generate electromagnetic waves at microwave frequencies and Radio wave and infrared frequencies. For this reason, Townes suggested replacing "microwave" with "molecular" as the first word in the acronym "maser".
The laser works by the same principle as the maser, but produces higher-frequency coherent radiation at Visible spectrum 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 , for "light amplification by stimulated emission of radiation". Gordon Gould is credited with creating this acronym in 1957.
Independently, Charles Hard Townes, James P. Gordon, and H. J. Zeiger built the first ammonia maser at Columbia University in 1953. This device used stimulated emission in a stream of energized ammonia molecules to produce amplification of microwaves at a frequency of about 24.0 hertz. Townes later worked with Arthur L. Schawlow to describe the principle of the optical maser, or laser, of which 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.
By putting such an amplifying medium in a resonant cavity, feedback is created that can produce coherent radiation.
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. Scientists use diamond in world's first continuous room-temperature solid-state maser, phys.org
During the early 1960s, the Jet Propulsion Laboratory developed a maser to provide ultra-low-noise amplification of S-band microwave signals received from deep space probes. 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 through a micrometer-adjustable entry to the chamber. The whole system noise temperature looking at cold sky (2.7 kelvin in the microwave band) was 17 kelvin. This gave such a low noise figure that the Mariner IV space probe could send still pictures from Mars back to the Earth, even though the output power of its radio transmitter was only 15 , and hence the total signal power received was only −169 with respect to a milliwatt (dBm).
Here is a brief description of how they work:
Extremely powerful masers, associated with active galactic nuclei, are known as and are up to a million times more powerful than stellar masers.
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, 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.
When the laser was developed, Townes and Arthur 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. In modern usage, devices that emit in the X-ray through infrared portions of the spectrum are typically called , 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 (gamma ray lasers), xasers (x-ray lasers), uvasers (ultraviolet lasers), lasers (visible light lasers), irasers (infrared lasers), masers (microwave masers), and rasers (radio frequency 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.
|
|
