Researchers have successfully demonstrated a laser that can transmit audio to a person via the air without wearing any type of special equipment.

The technique is based on photoacoustic effect using the water vapor to absorb light and create sound. According to the researchers, it can transmit various tones, music, and recorded speech at a conversational volume to a person at the other end of the room without anyone else hearing.

The details of the research were published in the journal Optics Letters by a team of researchers from MIT's Lincoln Lab, a research facility of the U.S. Department of Defense.

Using Laser To Transmit Audio

The technique can be done in two ways. The first approach grew from a technique called dynamic photoacoustic spectroscopy (DPAS) that involves sweeping the laser across an area at the speed of sound. To be able to encode different frequencies or audible pitches, the researchers altered the length of the laser sweeps.

The researchers explained that the approach can only be heard at a certain distance from a transmitter. It can only be heard by the intended recipient and not everyone who happens to cross the beam of light. It can also be used to transmit a targeted message to multiple people.

The second method, the traditional photoacoustic method, does not use the sweeping motion and instead creates different audios by modulating the power of the laser beam.

"There are tradeoffs between the two techniques," explained Ryan M. Sullenberger, the first author of the study. "The traditional photoacoustics method provides sound with higher fidelity, whereas the laser sweeping provides sound with louder audio."

The Handset-Free Future Of Communication

Inside the lab during testing, the first method transmitted audio to a person who was more than 2.5 meters away and at 60 decibels. The team hopes to continue testing the technology, next time taking the techniques outside and see how the range can be scaled up to.

"We hope that this will eventually become a commercial technology," shared Sullenberger. "There are a lot of exciting possibilities, and we want to develop the communication technology in ways that are useful."

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