New laser tech to send audible messages to specific person

A team of researchers from MIT has found a new way to transmit highly targeted audio signals directly to a person's ear using laser beams. The process known as "photoacoustic" is used for the system, which allows audible messages to be transmitted to spies or other agents, warning them of danger.

The researchers started with a laser beam that fired at wavelengths absorbed by water. By sweeping the beam, it was found that it could generate sound that can only be head at a specific distance from the transmitter. This allows the message to be sent to a specific person, rather than anyone who crosses the path of the beam.

"This can work even in relatively dry conditions because there is almost always a little water in the air, especially around people," said research lead Charles M. Wynn. "It is the first system that uses lasers that are fully safe for the eyes and skin to localize an audible signal to a particular person in any setting," he added.
The team has also found a method that works by modulating instead of sweeping the laser beam.

"There are tradeoffs between the two techniques," said researcher Ryan M. Sullenberger. "The traditional [modulation] method provides sound with higher fidelity, whereas the laser sweeping provides sound with louder audio."

As of now, the system works at more than 2.5 meters, so the scientists are planning to scale up the distance. "We hope that eventually, a commercial technology will develop," Sullenberger said.