British scientists have solved the decades-old problem of how to create a microwave laser that operates at room temperature — paving the way for a new generation of electronic sensors.
A maser (microwave amplification by stimulated emission of radiation) produces an amplified beam of microwaves similar to the visible light beam of a laser and can be used to make highly sensitive devices for detecting electromagnetic signals.
The researchers have become the first to produce masers that do not require very low temperatures, pressures or powerful magnets to operate, which could lead to their widespread use in a range of applications from radio telescopes to quantum computers.
Masers can be used to make very sensitive signal detectors because they introduce very low levels of background signal noise, said Dr Mark Oxborrow from the National Physical Laboratory (NPL), who developed the maser with colleagues from Imperial College London.
‘What a maser offers is low-noise performance and what low noise offers is sensitivity, and sensitivity can be important,’ he told The Engineer.
‘Sometimes it’s important to detect that weak signal that a spy is trying to transmit somewhere, or if a maser is used as the low-noise pre-amplifier in a body scanner then that might enable one to detect a disease that might otherwise not be detected.’
Traditional solid-state masers work by passing a microwave beam through a crystal gain medium such as ruby at temperatures close to absolute zero.
A second microwave beam at a different frequency, acting as what is known as a pumping mechanism, is used to excite the atoms in the gain medium, which then release energy as they return to their original state, amplifying the microwaves in the signal beam.
The NPL/Imperial team found it could create a solid-state maser that worked under ambient conditions using a crystal of the hydrocarbon p-terphenyl doped with pentacene and a pumping scheme of yellow optical light rather than the conventional method of using microwaves.
This produces a higher proportion of atoms in the upper energy level than with conventional masers, which have to be cooled dramatically using cryogenic refrigerators to prevent the atoms from falling back to the lower state too quickly.
The first masers were produced in the 1950s several years before lasers (which were originally called optical masers) but have had limited use ever since due to the high costs associated with the low temperatures or pressures needed to make them work.
Oxborrow said the potential for improving the new maser meant it should be able to compete with some modern semiconductor-based amplifiers, which have a similar performance to existing masers despite being a much more mature technology.
‘The crucial thing about the device we have created is that it’s a mark zero device,’ he said. ‘It has been put together on a very low budget, with lots of corners cut. And because it’s based on a completely different principle, no one really knows what the limits of performance are. No one really knows how good it could be if you improve things.’
Oxborrow added: ‘In a way, it does threaten the hegemony of the semiconductor industry.’
His colleague Prof Neil Alford of Imperial College London said in a statement: ‘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.’