For regular communication on Earth, this technology is rarely used because it only works at low temperatures. However, a research team at the London Centre for Nanotechnology and Saarland University has developed a maser that can be used at room temperature. Their development is described in the scientific journal "Nature," on March 22, 2018.
The abbreviation "maser" stands for "microwave amplification by stimulated emission of radiation," meaning microwave amplification generated by stimulated radiation emission. The physics behind the maser is similar to that of the laser, whose name stands for "light amplification by stimulated emission of radiation." Both generate coherent electromagnetic radiation at a single wavelength/frequency. "Until now, masers have been used primarily for communication in space, for example, to maintain radio contact with the Voyager spacecraft. Because masers can amplify very weak signals with almost no noise, this makes them interesting for future communication technologies on Earth," says Christopher Kay, Professor of Physical Chemistry and Chemistry Education at Saarland University.
One drawback of existing maser technology is that it requires very low temperatures, which can only be achieved using liquid helium. Together with other researchers at the London Centre for Nanotechnology, Christopher Kay has developed a maser that can operate at room temperature. The key to the technology is the use of a sapphire microwave resonator, held in a magnetic field. The resonator limits and concentrates the microwave radiation and can therefore be stably amplified into phase.
The radiation itself is generated by optically exciting "nitrogen vacancy" centers in a diamond. Unlike pure diamonds, which contain only carbon atoms and are therefore colorless, in the diamond used here, a small number of carbon atoms are replaced by a nitrogen atom. The space next to the nitrogen atom, which usually contains a carbon atom, is empty. "This defect is known as an NV (Nitrogen Vacancy) center and gives the diamond a purple color. It has a multitude of remarkable quantum properties and is therefore of interest for the development of new technologies, especially for nano-applications," explains Christopher Kay. For example, a maser can be used for more precise measurements in space exploration or nanotechnology, which is often called nanometrology. "Wherever low-intensity signals are received, for example, over long distances, and need to be amplified without adding noise, the maser opens up new possibilities," says Kay.
"It had already been suggested in the scientific community that NV-centered diamonds could be used as the basis for a maser, but the key to our success was placing a diamond in a sapphire resonator," explains the lead author of the Nature article, physicist Jonathan Breeze of Imperial College London. He added: "An interesting aspect of this technology is that the output frequency can be adjusted simply by changing the applied magnetic field. The current device operates at a frequency of 9 GHz (9 billion cycles per second). For comparison, mobile phones operate in the 2 GHz range. With commercially available magnetic technologies, frequencies of up to 200 GHz can be achieved with our room-temperature maser.".
As masers use optical photons to generate microwave photons, researchers hope their work will open new avenues in the fields of quantum diamond technology, magnetic resonance imaging, and communications.
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