Physicists at Imperial College London can now produce a continuous maser beam in room-temperature conditions. The set-up involves shining a laser light through a diamond, sapphire and copper apparatus to create the microwave emission.
The sensitivity of existing microwave amplifiers had been limited by background noise. The latest technique “pushes the noise of these amplifiers down while also allowing them to operate at room temperature”, says David Awschalom, a physicist at the University of Chicago in Illinois, who was not involved in the research. “This work is very exciting.”
Diamond Age of Masers
The research, published in Nature on 21 March, builds on a system made in 2012 by members of the same team. That device also worked at room temperature but it produced only maser pulses, which are less useful than a continuous beam. The team solved that problem by replacing a key component of the set-up called the gain medium. The first device used an organic molecule called pentacene, which degraded over time. In the new instrument, they inserted a tiny diamond created under particular conditions, which was more stable and produced non-stop radiation.
The latest maser is still just a proof of principle and will require improvements in its power and stability to match existing devices, says Ren-Bao Liu, a physicist at the Chinese University of Hong Kong. But it could benefit fields that currently use low-temperature amplifiers, by creating cheaper, more-convenient devices, he says. Moreover, its exploitation of a feature of the diamond that was used — small defects known as nitrogen-vacancy centres — means it might also find applications in quantum technologies that also take advantage of those imperfections
The maser—the microwave progenitor of the optical laser—has been confined to relative obscurity owing to its reliance on cryogenic refrigeration and high-vacuum systems. Despite this, it has found application in deep-space communications and radio astronomy owing to its unparalleled performance as a low-noise amplifier and oscillator. The recent demonstration of a room-temperature solid-state maser that utilizes polarized electron populations within the triplet states of photo-excited pentacene molecules in a p-terphenyl host paves the way for a new class of maser. However, p-terphenyl has poor thermal and mechanical properties, and the decay rates of the triplet sublevel of pentacene mean that only pulsed maser operation has been observed in this system. Alternative materials are therefore required to achieve continuous emission: inorganic materials that contain spin defects, such as diamond and silicon carbide, have been proposed. Here we report a continuous-wave room-temperature maser oscillator using optically pumped nitrogen–vacancy defect centres in diamond. This demonstration highlights the potential of room-temperature solid-state masers for use in a new generation of microwave devices that could find application in medicine, security, sensing and quantum technologies.