Laser’s Cousin Comes In from the Cold

A new solid-state maser capable of operating at room temperature could enable more sensitive medical instruments, improved chemical sensors, and better radio telescopes, among other applications.

A team in England replaced the maser’s ruby with a different type of crystal (pentacene-doped p-terphenyl) that allows masing in a solid-state device working at room temperature with no applied magnetic field. The breakthrough could make maser use as common as lasers. Shown here is the core: a pink crystal surrounded by a clear sapphire ring. (Images: NPL)

The maser (microwave amplification by stimulated emission of radiation) was developed more than 50 years ago, before the first lasers were invented. Unlike lasers, which create intense beams of light, masers deliver concentrated beams of microwaves using crystals such as ruby.

Compared with lasers, the maser has had little technological impact because getting it to work requires difficult-to-produce conditions — either extremely low pressures, supplied by special vacuum chambers and pumps, or freezing conditions at temperatures close to absolute zero, supplied by special refrigerators. In addition, the application of a strong magnetic field is necessary, requiring large magnets.

Now, scientists from the National Physical Laboratory and Imperial College London have demonstrated masing in a solid-state device working in air at room temperature with no applied magnetic field. The breakthrough could dramatically reduce the cost to manufacture and operate masers, which could lead to their being used as commonly as lasers.

The first recorded burst of maser oscillation. The vertical axis is output power on a logarithmic scale, where the top of the screen is 20 dBm (0.1 W) and the bottom of the screen is –60 dBm (1 nW). The horizontal axis is time where the full horizontal span of the screen corresponds to a duration of 1 ms.

“For half a century, the maser has been the forgotten, inconvenient cousin of the laser,” said Dr. Mark Oxborrow of NPL, co-author of the study. “Our design breakthrough will enable masers to be used by industry and consumers.”

Although conventional maser technology works by amplifying microwaves using hard inorganic crystals such as ruby — which must be kept at very low temperatures — the team discovered that a completely different type of crystal – p-terphenyl doped with pentacene – could replace ruby and replicate the same masing at room temperature. It not only replicates the masing process, but also turns the otherwise colorless p-terphenyl an intense reddish pink — making it look just like a ruby, the scientists say.

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 readout mechanisms for quantum computers and better radio telescopes for potentially detecting life on other planets.

Mark Oxborrow holds the maser core outside the National Physical Laboratory in Teddington.

Before the maser can be applied to such technologies, the researchers must tackle a few challenges, including getting the device to work continuously. It currently works only 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 wants to identify other materials that could mase at room temperature while consuming less power than pentacene-doped p-terphenyl. A smaller and more portable maser also is on the horizon.

“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,” said professor Neil Alford, head of the Department of Materials at Imperial College London and co-author of the study. “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.”

The research, funded by the Engineering and Physical Sciences Research Council and the UK’s National Measurement Office, was published Aug. 16 in Nature.

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