Navy Scientists Develop Laser For Underwater Communication

Researchers at the Naval Research Laboratory claim to have come up with a better tool for underwater acoustics. The new system uses laser light to create sound underwater from a distance. This technology could allow planes a much easier method of communicating with submarines without the need for a floating buoy. "Efficient conversion of light into sound can be achieved by concentrating the light sufficiently to ionize a small amount of water, which then absorbs laser energy and superheats. The result is a small explosion of steam, which can generate a 220 decibel pulse of sound. Optical properties of water can be manipulated with very intense laser light to act like a focusing lens, allowing nonlinear self-focusing (NSF) to take place. In addition, the slightly different colors of the laser, which travel at different speeds in water due to group velocity dispersion (GVD), can be arranged so that the pulse also compresses in time as it travels through water, further concentrating the light. By using a combination of GVD and NSF, controlled underwater compression of optical pulses can be attained."

Comments

And the things living around it?

[Anonymous Coward]

I wonder how many marine animals we'll cause to go deaf from this, which would probably end any chance of survival for those affected. http://www.makeitlouder.com/Decibel%20Level%20Chart.txt 220 decibels is incredibly loud in the air, I can only guess the extended intensity it travel with underwater...

Re:And the things living around it?

[Anonymous Coward]

You are mixing up apples and oranges. The dB level in the water is not directly related to the dB level in the air. As Discovery of Sound in the Sea says:

Confusion arises because relative sound intensities given in dB in water are not directly comparable to relative sound intensities given in dB in air.

... The result is that sound waves with the same intensities in water and air when measured in watts per square meter have relative intensities that differ by 61.5 dB. This amount must be subtracted from relative intensities in water referenced to 1 microPascal (ÂPa) to obtain the relative intensities of sound waves in air referenced to 20 microPascals (ÂPa) that have the same absolute intensity in watts per square meter.

Re:Whale/sonar people are going to love this one

[fluffy99]

Active Sonar output is limited by cavitation. That is the boiling of the water on the surface of the transducer, which acts like a blanket attenuating and distorting the output. In general that means under 200 dB. Still plenty to cause problems with local wildlife. Active sonar is not used very often at its also like turning on a spotlight in a dark room.

Re:Operational security?

[cwebster]

The issue isnt eavesdropping, its that the mere act of communicating gives your position away to everyone when wants to know.

Re:How does this NOT pose a danger...

[John Hasler]

Swimmers would be in about the same danger of being zapped by this thing as they would of being hit on the head by one of the air-dropped buoys that it would replace.

Re:Operational security?

[ceoyoyo]

Dropping a sonobuoy and transmitting a message tends to have the same effect.

There are apparently circumstances when you need to have a chat with a submarine and it's worth giving away that there's a sub somewhere within X km, in some direction. On the other hand, since you don't have to drop a buoy every time, with the laser system you could potentially go around broadcasting some dummy messages too.

Re:How does this NOT pose a danger...

[Mozk]

Interesting note: it also occurs the other way around with sonoluminescence. Intense sound through a liquid can create light.