‘Sound laser’ is the most powerful ever made

A tiny, levitated bead is at the core of an unprecedentedly bright laser that shoots particles of sound instead of light.

Just as a ray of light is made up of many particles called photons, sound consists of particle-like chunks called phonons. For several decades, researchers have been creating “phonon lasers” that output these particles in a narrow beam, similar to the way optical lasers emit photons.

Now, Hui Jing at Hunan Normal University in China and his colleagues have created the brightest phonon laser yet.

The heart of their device was a roughly micrometre-long silica bead, about the size of a typical bacterium. They used two beams of light to levitate the bead and surrounded it with a reflective cavity. Any small vibration of this bead created phonons, which were then trapped and amplified in the cavity. This continued until there were enough phonons to make up a laser-like beam.

Several research groups had tested similar designs before. But Jing and his colleagues added an electrode right below the bead, which produced carefully selected electromagnetic signals. This modification enhanced the laser’s “brightness” – the amount of power it delivered at each phonon frequency – tenfold, as well as making its beam tighter and helping it last longer. Jing says that past devices, from his team and others, worked for dozens of minutes only, but the latest phonon laser could operate for over an hour.

Phonons are less affected by moving through liquids, so they could be more effective than conventional lasers for imaging watery tissues in biomedicine or in some deep-sea monitoring devices, Jing says.

But Richard Norte at the the Delft University of Technology in the Netherlands says current experimental set-ups, which require precise tuning of every component, are too intricate. Phonon lasers may require years of research and engineering before they match the usefulness of their optical counterparts.

“There is excitement about phonon lasers given the impact that optical lasers have had on modern life, but time will tell if there will be an equivalent impact,” he says.