Laser Fundamentals

An unknowing recipient of such messages would think that they had gone insane.

Of course, they’ll only use their powers for good.

 

Don’t worry, though. According to MIT, this technology will only be used to help humanity. Yep.

 

    They believe further research will allow them to scale up the transmission distance, which could make the technique useful in dangerous situations, such during a mass shooting — authorities could beam instructions directly to individuals without anyone else hearing them.

 

    “We hope that this will eventually become a commercial technology,” researcher Ryan M. Sullenberger said. “There are a lot of exciting possibilities, and we want to develop the communication technology in ways that are useful.” (source)

 

Think about it –  susceptible people could literally be convinced they were hearing the voice of God.

 

Talk about someone getting in your head.

 

Scientists have figured out how to use a laser to transmit audio, ranging from music to speech, to a person across a room without any receiver equipment — a potential breakthrough for the future of audio and communication.

 

“Our system can be used from some distance away to beam information directly to someone’s ear,” Massachusetts Institute of Technology research Charles M. Wynn said in a press release. “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.”

 

Sweeping Success

In a paper published on Friday in the journal Optics Letters, the MIT team describes how it developed two different methods to transmit tones, music, and recorded speech via a laser.

 

Both techniques take advantage of something called the photoacoustic effect, which is the formation of sound waves as the result of a material absorbing light. In the case of the MIT research, that material was water vapor in the air.

 

For one of their methods, the researchers “swept” a laser beam at the speed of sound, changing the length of the sweeps to encode different audible pitches.

 

This technique allowed them to transmit sound to a person more than 8.2 feet away at a volume of 60 decibels — about the loudness of background music or a conversation in a restaurant — without anyone between the source of the sound and the target hearing it.

 

For the other method, they encoded an audio message by adjusting a laser beam’s power. They said this technique produced a quieter but clearer result.

 

Psst

As cool as it would be to use a laser to sneak a message to a friend across a crowded room, the MIT team has far more important applications in mind for its technology.

They believe further research will allow them to scale up the transmission distance, which could make the technique useful in dangerous situations, such during a mass shooting — authorities could beam instructions directly to individuals without anyone else hearing them.

 

“We hope that this will eventually become a commercial technology,” researcher Ryan M. Sullenberger said. “There are a lot of exciting possibilities, and we want to develop the communication technology in ways that are useful.”

New Technology Uses Lasers to Transmit Audible Messages to Specific People

Photoacoustic communication approach could send warning messages through the air without requiring a receiving device

 

 

New Technology Uses Lasers to Transmit Audible Messages to Specific People

Photoacoustic communication approach could send warning messages through the air without requiring a receiving device

 

WASHINGTON — 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.

 

“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 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.

 

“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.

 

“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.”

 

Paper: R. M. Sullenberger, S. Kaushik, C. M. Wynn. “Photoacoustic communications: delivering audible signals via absorption of light by atmospheric H2O,” Opt. Lett., 44, 3, 622-625 (2019).

DOI: https://doi.org/10.1364/OL.44.000622.

 

About Optics Letters

Optics Letters offers rapid dissemination of new results in all areas of optics with short, original, peer-reviewed communications. Optics Letters covers the latest research in optical science, including optical measurements, optical components and devices, atmospheric optics, biomedical optics, Fourier optics, integrated optics, optical processing, optoelectronics, lasers, nonlinear optics, optical storage and holography, optical coherence, polarization, quantum electronics, ultrafast optical phenomena, photonic crystals and fiber optics.

 

About The Optical Society

 

Founded in 1916, The Optical Society (OSA) is the leading professional organization for scientists, engineers, students and business leaders who fuel discoveries, shape real-life applications and accelerate achievements in the science of light. Through world-renowned publications, meetings and membership initiatives, OSA provides quality research, inspired interactions and dedicated resources for its extensive global network of optics and photonics experts. For more information, visit osa.org.

 

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MIT Has Invented Slightly Eerie Lasers That Transmit Whispers Only You Can Hear

 

 

MIKE MCRAE 25 JAN 2019

New technology being developed by the MIT's Lincoln Laboratory uses laser light to excite moisture in the air surrounding a target's ear, causing it to quietly whisper a personal message from several metres away.

 

"Our system can be used from some distance away to beam information directly to someone's ear," says MIT team leader and physicist Charles M. Wynn.

 

You probably don't need us to count off potential applications for such a device, which range from military applications to targeted advertising.

 

Pretty much anywhere ambient noise is a problem - or earphones are unsuitable - a laser-tongued whisper could do the job.

 

In case you're worried about the whole 'laser in your ear' thing, the developers promise it's harmless.

 

"It is the first system that uses lasers that are fully safe for the eyes and skin to localise an audible signal to a particular person in any setting," says Wynn.

 

Technology that channels sound into a narrow field has been around for decades.

 

Most of it uses speakers to intensify soundwaves or channel ultrasound within a small area. Although useful for keeping sound relatively confined, they require the listener to be a relatively short distance from the source.

 

Optical technology based on lasers has the potential advantage of reduced spreading over a distance, with higher frequencies allowing it to carry much further – which is why the team have turned from speakers to lasers.

 

The heart of MIT's new technology is a 1.9 micrometre thulium laser. Thanks to a principle called the photoacoustic effect, water vapour in the air absorbs the laser's emission, causing it to vibrate at an audible frequency.

 

"This can work even in relatively dry conditions because there is almost always a little water in the air, especially around people," says 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."

 

The team tested two methods for transmitting sound. The first simply varied the laser's amplitude through a modulator in a continuous wave, creating vibrations that could be picked up by a microphone 2.5 metres (8 feet) away.

 

A second process ditched the modulator and used a mirror to sweep the laser back and forth over at the speed of sound in what's known as dynamic photoacoustic spectroscopy, effectively creating louder waves by jiggling more water particles.

 

"There are trade-offs between the two techniques," says opto-mechanical engineer Ryan M. Sullenberger.

 

"The traditional photoacoustics method provides sound with higher fidelity, whereas the laser sweeping provides sound with louder audio."

 

A potential disadvantage of the laser-wiggle method is it works at a very specific distance from the transmitter. Any closer, and the laser's sweep will be too high-pitched. Any further, and the frequency drops below audibility.

 

Although it was only tested to a volume of 60 decibels (the level of a normal conversation) at a couple of metres, the researchers think they can scale up the distance and volume now they have proof of concept.

 

"We hope that this will eventually become a commercial technology," says Sullenberger.

 

Which means in future someone could potentially beam whispers to your ear from significant distances... something that's both slightly unnerving and exciting at the same time.

 

This research was published in OSA Publishing.