Before lasers, there were masers — the microwave siblings of optical lasers. But whereas lasers are used in many applications from telescopes to medicine, masers have long languished in the shadows, because they work only in super-cool temperatures or in a vacuum. Now, physicists have created a maser that works in regular conditions — using diamond.

Masers, which were conceived in the 1950s, and lasers, which followed in 1960, generate intense beams of highly ordered electromagnetic waves. Masers can be used to amplify tiny traces of radiation with little noise, making them useful for measuring weak signals in astronomy and for communicating with distant missions, such as NASA’s Voyager probes. But these applications usually require cryogenic cooling. In some cases, microwave devices could be more useful than lasers because microwaves can pass through materials than optical light can’t.

The latest device, made by 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 (see video).

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.”

The research, published in Nature on 21 March1, 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, he says.