Few laypeople, perhaps, know the term “light amplification by stimulated emission of radiation”, although everyone knows the technology by its familiar name, the laser. And “microwave amplification of stimulated emission of radiation”, or maser, is much more obscure – despite having been invented more than 50 years ago before the laser.
Could we one day be talking of masers as familiarly as we do of lasers? There are reasons why the technology has not developed to attain the ubiquity of the latter. Getting a maser to work has required a lot of equipment: either extremely low pressures supplied by special vacuum chambers and pumps, or freezing conditions at temperatures close to absolute zero (-273.15°C). With these constraints, the maser, which delivers a concentrated beam of microwaves as opposed to light, has never been able to develop in the manner of its laser cousin.
But scientists at the National Physical Laboratory and Imperial College London believe this could change. In the summer they reported a milestone in research into masers, which could herald a new phase of industrial development for the technology. The breakthrough does indeed seem significant, because the scientists were able to demonstrate a solid-state maser that operated at room temperature, working in air and with no applied magnetic field.
This means the technology could be miniaturised and made portable, without the need for bulky refrigeration equipment. Future applications could include more sensitive body scanners that could detect small tumours or hidden explosives, more sensitive radar, and sensitive radio telescopes.
Previously, getting results from the maser was a tough job, says Dr Mark Oxborrow, co-author of the NPL study on the solid-state maser. “To get the maser to work it had to sit in the bottom of a big refrigerator just to get it down to close to absolute zero. So the paraphernalia that you needed just to sustain this amplifier was expensive, and big and bulky. It wasn’t possible to make a mobile amplifier because it consumed too much electricity, or needed to be supplied with cryogenic fluids from time to time.”
Most of the applications of masers are as amplifiers, says Oxborrow. They work by amplifying electromagnetic signals, with the advantage that they are very low noise. “Only in extreme situations – where one was prepared to pay anything to get a slightly lower noise amplifier – were masers viable.”
This does not mean that they have not been used. For example, Nasa still uses masers to detect signals coming from deep space. “A maser is good at amplifying weak signals,” he says. “When you have a small signal coming, an amplified copy of that signal comes out – and if you didn’t have a low noise amplifier, the output would contain noise and fuzz.”
Oxborrow adds: “When we get data back from the Curiosity rover [which is exploring Mars], the signal back on Earth is tiny, really puny. The satellite picking up the signal from the surface of Mars only has solar cells, and not much to power its transponder. When the signal reaches home, it’s the order of -210dBm. You need to amplify it to a useful level without introducing a huge amount of noise. That’s why masers are still in use by Nasa today to boost signals from distant space probes – despite the cryogenic problem.”