Using the photoacoustic effect, researchers demonstrated that a laser could transmit an audible message to a person without using any receiver equipment. The ability to send highly targeted audio signals over the air could be helpful to communicate across noisy rooms or to alert people to a potentially dangerous situation, such as an active shooter.
The researchers used two laser-based methods to transmit tones, music, and recorded speech at a conversational volume. The system can beam information directly to someone’s ear from a distance. It is the first system that uses lasers that are completely safe for the eyes and skin to pinpoint an audible signal to a specific person in any environment.
The new approaches leverage the photoacoustic effect, which occurs when a material absorbs light and produces sound waves. In this case, the researchers used airborne water vapor to absorb light and generate sound.
Because there is almost always a little water in the air, especially around people, the effect can work even in relatively dry conditions. If the researchers use a laser wavelength very strongly absorbed by water, they won’t need much water. It was critical because more absorption results in more sound. The researchers intend to demonstrate the methods outdoors at greater distances.