16 August 2012

Advances in MASER Technology Aligns It With LASER Technology

In each frame, a molecule in the upper level of the MASER transition (that is, in the high energy, excited state) is indicated by a large red circle, while one in the lower level (low energy state) is indicated by a small blue circle. (a) All of the molecules are in the upper state and a photon of wavelength l (shown in green) is incident from the left. (b) The photon l stimulates emission from the first molecule, so there are now two photons of wavelength l, in phase. (c) These photons stimulate emission from the next two molecules, resulting in four photons of wavelength l. (d) The process continues with another doubling of the number of photons.
Credit: Stanford University/M. L. Kutner, "Astronomy: A Physical Perspective", John Wiley & Sons, Inc. 1987

MASER is an acronym for Microwave Amplification by Stimulation Emission of Radiation. It is a device that produces coherent electromagnetic waves through amplification by stimulated emission. Coherent waves are two or more waves that generate waves at the same time, having the same frequency, amplitude, and phase.

During the development of the MASER, it was found that masers emit EM waves which are in the microwave and radio frequencies across a broader band of the electromagnetic spectrum. To maintain the accuracy of the acronym, it was suggested that the letter "M" stand for molecular rather than microwave.

A LASER is a type of MASER that works with photons at a higher frequency in the ultraviolet or visible light spectrum. In 1957, with the development of the optical coherent oscillator, the LASER was first called an optical maser. It eventually was called a LASER (Light Amplification by Stimulated Emission of Radiation), the name coined by Gordon Gould in 1957.

It was Albert Einstein who proposed the principle of stimulated emission in which the MASER was based. Einstein proposed that when atoms are induced into an excited energy state, these 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.

MASER power comes out of the cold

Scientists demonstrate, for the time, a solid-state "MASER" capable of operating at room temperature, paving the way for its widespread adoption – as reported today in the journal Nature.

MASER stands for Microwave Amplification by Stimulated Emission of Radiation. Devices based on this process (and known by the same acronym) were developed by scientists more than 50 years ago, before the first LASERs were invented. Instead of creating intense beams of light, as in the case of LASERs, MASERs deliver a concentrated beam of microwaves.

Conventional MASER technology works by amplifying microwaves using hard inorganic crystals such as ruby, this process is known as "masing". However, the MASER has had little technological impact compared to the LASER because getting it to work has always required extreme conditions that are difficult to produce; either extremely low pressures, supplied by special vacuum chambers and pumps, or freezing conditions at temperatures close to absolute zero ( -273.15°C), supplied by special refrigerators. To make matters worse, the application of strong magnetic fields has often also been necessary, requiring large magnets.

Now, the team from the National Physical Laboratory (NPL) and Imperial College London have demonstrated masing in a solid-state device working in air at room temperature with no applied magnetic field. Today's breakthrough means that the cost to manufacture and operate MASERs could be dramatically reduced, which could lead to them becoming as widely used as LASER technology.

The researchers suggest that room-temperature MASERs could be used to make more sensitive medical instruments for scanning patients, improved chemical sensors for remotely detecting explosives; lower-noise read-out mechanisms for quantum computers and better radio telescopes for potentially detecting life on other planets.

Video: AT&T Archives: Principles of the Optical Maser

Dr Mark Oxborrow, co-author of the study at NPL, says: "For half a century the MASER has been the forgotten, inconvenient cousin of the LASER. Our design breakthrough will enable MASERs to be used by industry and consumers."

Professor Neil Alford, co-author and Head of the Department of Materials at Imperial College London, adds: "When LASERs were invented no one quite knew exactly how they would be used, and yet the technology flourished to the point that LASERs have now become ubiquitous in our everyday lives. We've still got a long way to go before the MASER reaches that level, but our breakthrough does mean that this technology can literally come out of the cold and start becoming more useful."

Conventional MASER technology using hard inorganic crystals such as ruby, only works when the ruby is kept at a very low temperature. The team in today's study have discovered that a completely different type of crystal, namely p-terphenyl doped with pentacene, can replace ruby and replicate the same masing process at room temperature.

As a curious twist, the pentacene dopant turns the otherwise colourless p-terphenyl crystal an intense reddish pink – making it look just like ruby!

The twin challenges the team currently face are getting the MASER to work continuously, as their first device only works in pulsed mode for fractions of a second at a time. They also aim to get it to operate over a range of microwave frequencies, instead of its current narrow bandwidth, which would make the technology more useful.

In the long-term, the team have a range of other goals including the identification of different materials that can mase at room temperature while consuming less power than pentacene-doped p-terphenyl. The team will also focus on creating new designs that could make the MASER smaller and more portable.


National Physical Laboratory
Imperial College London
Room-temperature Solid-state Maser
What is a MASER?
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