The new technology, developed by Lincoln's Massachusetts Institute of Technology, uses laser light to excite the humidity in the air around the target's ear, resulting in a quiet whisper of a few meters of personal message.
"Our system can be used remotely to broadcast information directly to someone's ear," says the head of the MIT team and physicist Charles Wynn.
Probably, you do not need to count potential apps for a device that range from military applications to targeted ads.
Almost everywhere where environmental noise is a problem – or the headphones are inappropriate – a laser whisper can do the job.
If you worry about the entire laser in your ear, the developers promise it is harmless.
"This is the first system that uses lasers that are completely safe for the eyes and skin to locate a beep to a particular person in any environment," Wynn says.
The technology that channels the sound in a narrow area has existed for decades.
Most of them use loudspeakers to amplify sound waves or ultrasound channel in a small area. Although useful for keeping the volume relatively limited, they require the listener to be at a relatively short distance from the source.
Laser-based optical technology has the potential advantage of reduced scattering at higher frequencies that allow it to carry much more – so the team has turned from speakers to lasers.
The heart of MIT's new technology is a 1.9 micrometer tall laser. Thanks to the principle called photoacoustic effect, the water vapor in the air absorbs the emission of the laser, resulting in vibration of the sound frequency.
"It can work even in relatively dry conditions, because there is almost always little water in the air, especially around people," Wynn says.
"We have found that we do not need much water if we use a laser wavelength that is highly absorbed by the water, which is the key because stronger absorption leads to more sound."
The team tested two methods of transmitting sound. The first simply changes the laser amplitude through a continuous wave modulator, creating vibrations that can be taken from a 2.5 meter (8 feet) microphone.
The second process left the modulator and used a mirror to widen the laser back and forth at the speed of sound in the so-called dynamic photoacoustic spectroscopy, effectively creating stronger waves by stirring more water particles.
"Between the two techniques there are compromises," says optomether engineer Ryan M. Sullenberger.
"The traditional photoacoustic method provides higher precision sound while laser sweep provides sound with louder sound."
A potential drawback of the laser shuffling method is that it operates at a very specific distance from the transmitter. Any closer, and the laser will be too high. Anyone further down and the frequency falls under audibility.
Although tested only with a volume of 60 decibels (the level of a normal conversation) a few meters, researchers believe they can increase the distance and volume now that they have proof of the concept.
"We hope this will eventually become a trading technology," says Sullenberger.
Which means that in the future someone could emit hearing rumors at considerable distances … something that is both slightly disturbing and exciting at the same time.
This study was published in OSA Publishing House,