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Researchers have demonstrated that a laser can transmit an audible message to a person without any type of receiver equipment. The ability to send highly targeted audio signals over the air could be used to communicate across noisy rooms or warn individuals of a dangerous situation such as an active shooter.
In The Optical Society (OSA) journal Optics Letters, researchers from the Massachusetts Institute of Technology's Lincoln Laboratory report using two different laser-based methods to transmit various tones, music and recorded speech at a conversational volume.
System - Distance - Information - Someone - Ear
"Our system can be used from some distance away to beam information directly to someone's ear," said research team leader 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."
The new approaches are based on the photoacoustic effect, which occurs when a material forms sound waves after absorbing light. In this case, the researchers used water vapor in the air to absorb light and create sound.
Conditions - Water - Air - People - Wynn
"This can work even in relatively dry conditions because there is almost always a little water in the air, especially around people," said Wynn. "We found that we don't need a lot of water if we use a laser wavelength that is very strongly absorbed by water. This was key because the stronger absorption leads to more sound."
One of the new sound transmission methods grew from a technique called dynamic photoacoustic spectroscopy (DPAS), which the researchers previously developed for chemical detection. In the earlier work, they discovered that scanning, or sweeping, a laser beam at the speed of sound could improve chemical detection.
Speed - Sound - Speed
"The speed of sound is a very special speed at...
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