New technology uses lasers to transmit audible messages to specific people

January 23, 2019, Optical Society of America
Credit: CC0 Public Domain

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 -based methods to transmit various tones, music and recorded speech at a conversational volume.

"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."

Creating sound from air

The new approaches are based on the , which occurs when a material forms waves after absorbing light. In this case, the researchers used in the air to absorb light and create sound.

"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 at the could improve chemical detection.

"The speed of sound is a very special speed at which to work," said Ryan M. Sullenberger, first author of the paper. "In this new paper, we show that sweeping a laser beam at the speed of sound at a wavelength absorbed by water can be used as an efficient way to create sound."

For the DPAS-related approach, the researchers change the length of the laser sweeps to encode different frequencies, or audible pitches, in the light. One unique aspect of this laser sweeping technique is that the signal can only be heard at a certain distance from the transmitter. This means that a message could be sent to an individual, rather than everyone who crosses the beam of light. It also opens the possibility of targeting a message to multiple individuals.

Laboratory tests

In the lab, the researchers showed that commercially available equipment could transmit sound to a person more than 2.5 meters away at 60 decibels using the laser sweeping technique. They believe that the system could be easily scaled up to longer distances. They also tested a traditional photoacoustic method that doesn't require sweeping the laser and encodes the audio message by modulating the power of the laser beam.

"There are tradeoffs between the two techniques," said Sullenberger. "The traditional photoacoustics method provides sound with higher fidelity, whereas the laser sweeping provides sound with louder audio."

Next, the researchers plan to demonstrate the methods outdoors at longer ranges. "We hope that this will eventually become a commercial technology," said Sullenberger. "There are a lot of exciting possibilities, and we want to develop the communication technology in ways that are useful."

Explore further: New photoacoustic technique detects gases at parts-per-quadrillion level

More information: Ryan M. Sullenberger et al, Photoacoustic communications: delivering audible signals via absorption of light by atmospheric H2O, Optics Letters (2019). DOI: 10.1364/OL.44.000622

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10 comments

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Spaced out Engineer
1 / 5 (4) Jan 23, 2019
LIKE sleep depriving people through the walls of their home!
https://www.bigge...den.com/
Yay!
TheGhostofOtto1923
1 / 5 (2) Jan 23, 2019
Whats that? Did you hear that?? No? But it was as clear as a bell, like someone was standing right next to me... Gawd I must be losing my mind...

Like MKUltra
Phyllis Harmonic
5 / 5 (3) Jan 23, 2019
The paper is open for all: https://www.osapu...d=404226

Interesting work- so far it's only tones being transmitted but they hint at higher fidelity (e.g. speech and music).
Phyllis Harmonic
1 / 5 (1) Jan 23, 2019
Deleted yet another duplicate!
Phyllis Harmonic
1 / 5 (1) Jan 23, 2019
Deleted duplicate
Phyllis Harmonic
1 / 5 (1) Jan 23, 2019
Deleted duplicate
FredJose
1 / 5 (4) Jan 24, 2019
Interesting! Of course being able to generate sound waves leaves the door wide open for building acoustic WEAPONS - the usual money spinner cannot be far behind. So then the perpetrator can select and hit the target without anyone else being the wiser. No loud bang, no bullet marks, no blood spatter, nothing. Just a person lying dead on the ground etc. Not a pleasant thought and unfortunately one of the first things the sinful human race will hanker after.
antialias_physorg
1 / 5 (1) Jan 24, 2019
or warn individuals of a dangerous situation such as an active shooter.

That seems....oddly specific. And also I can't grok any situation where that would actually be more useful than, say, blasting the warning over a PA system.

(Also: is silently warning people about active shooters a use case anywhere in the world? I would have thought that hearing shots being fired would do that just fine.)
TheGhostofOtto1923
not rated yet Jan 24, 2019
Interesting! Of course being able to generate sound waves leaves the door wide open for building acoustic WEAPONS
Oh, weapons dont have to be LOUD to injure and destroy...

"And your ears shall hear a word behind you, saying, "This is the way, walk in it," when you turn to the right or when you turn to the left." Isaiah 30:21

-Per my above post, what if people actually started to hear god talking to them?

"22 Some time later God tested Abraham. He said to him, "Abraham!"

"Here I am," he replied.

2 Then God said, "Take your son, your only son, whom you love—Isaac—and go to the region of Moriah. Sacrifice him there as a burnt offering on a mountain I will show you." gen22
Da Schneib
1 / 5 (1) Jan 28, 2019
Gee, haven't we been hearing about a bunch of diplomats in Cuba who heard stuff and got brain damaged?

Wonder how many dissidents they tested it on before they deployed it?

I mean, just askin'.

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