Scientists have successfully built a laser that uses sound waves instead of light.
Lasers, which stand for "light amplification by stimulated emission of radiation," have almost always used light waves since their conception over 50 years ago. They are created when a group of light particles, called photons, are emitted at a specific and narrow wavelength. Since the new lasers are comprised of sound particles called phonons, they should actually be termed phasers.
Scientists proposed the idea of sound wave-based lasers during the invention's early stages. The idea proved elusive until 2010, when scientists created the first sound lasers. They were hybrid devices, whereby light from a traditional laser was used to create sound emissions. The new sound-based laser, however, marks a departure from this method.
"In our work, we got rid of this optical part," says engineer Imran Mahboob of NTT Basic Research Laboratories in Japan, who co-authored a paper detailing the new laser that appears Monday March 18 in "Physical Review Letters." According to Mahboob, the new phasers are "much easier to integrate into other applications and devices."
The new device works through a mechanical oscillator. The oscillator excites photons, which then relax, resulting in their energy returning back to the device. Because of the confined energy, the phaser vibrates, resulting in the production of phonons. The contraption is engraved onto an integrated circuit with dimensions of about one cm by 0.5 cm.
One drawback to the phaser, however, is that it cannot travel through a vacuum. This marks a difference from the traditional laser and confines it to the device itself for now.
"We would lose the lasing if we get it out," Mahboob says. "So we will need to figure out how to build structures onto the resonator that would allow us to transmit the vibrations out as energy."
That said, there are a number of potential applications for the phaser. Part of the contraption turns mechanical vibration into an oscillating electrical signal, which could be used as a small clock. Upon further development, ultrasound frequencies could be used for scanning objects or people for medical reasons. It could also be used for high-precision measurement.
"It's still in its infancy," says Johns Hopkins University engineer Jacob Khurgin, "but they showed it can be done, and more people will get involved."