Just imagine that you are in a serious negotiation meeting and could communicate important tactics with your colleague on the other side of the negotiation table or room by secretly whispering into his or her ear without anybody else knowing or hearing it writes Prof Louis C H Fourie.
JOHANNESBURG - Just imagine that you are in a serious negotiation meeting and could communicate important tactics with your colleague on the other side of the negotiation table or room by secretly whispering into his or her ear without anybody else knowing or hearing it.

This is exactly what scientists at the Massachusetts Institute of Technology (MIT) in Boston, USA, achieved when they developed a laser light system to send secret sound messages across a room. Earlier this year they published an article in the scientific journal Optic Letters under the title “Photoacoustic communications: delivering audible signals via absorption of light by atmospheric H2O.” In the article they describe a method of communication in which a person with no external receiver hears an audible audio message directed only at him or her.

The message is encoded and sent upon a modulated 1.9 micrometer thulium laser beam directly to the receiver’s ear by making use of the photoacoustic effect. Through the use of a fast-twitching mirror the laser is wiggled back and forth across the water molecules in the air by someone's ear. The wiggling jolts the molecules into motion, causing them to bang against the surrounding air molecules and produce sound waves that could only be heard by the receiver.

The particular laser wavelength used by the researchers is very strongly absorbed by water and therefore does not need much atmospheric water. The technology can even work in relatively dry conditions since there is almost always a little water in the air.

The underlying concept is not totally new. The famous Alexander Graham Bell, who is the inventor of the first practical telephone, patented a device that transmitted sounds via light already in 1880 along with his partner Charles Sumner Tainter. This "photophone-transmitter" was a proposed instrument to control a light beam so that when it reached a receiver instrument it would produce sound.

In more understandable language: If light is wiggled over some material sound should be generated. The key differences between the Bell/Tainter proposed device and the modern MIT device are that the receiver material is just ambient water vapour, and that the light is a precision laser. But the underlying concept is the same.

The MIT scientists are also not the first to transmit sound waves using lasers, but their method produces the loudest sound. There are currently other methods under development that produce much clearer sounds, but these methods (like switching a laser on and off extremely fast to jiggle the water molecules) do not make sounds as loud as the wiggling or sweeping method.

The eventual aim of the MIT research is to send messages to individuals in an outdoor crowd or at much longer ranges without having to broadcast the (sometimes confidential) messages over loudspeakers for everybody to hear. The ability to beam highly targeted audio signals over the air could be used to communicate across noisy rooms or in public places where the need exists to warn individuals of a dangerous situation such as a shooting, heist or other immanent crisis.

It is this longer-range communication that interests the military. In the USA laser-sound weapons are being developed as part of a military initiative called the Joint Non-Lethal Weapons Directorate (JNLWP). The aim of the project is to create laser weapons that could transmit short pieces of human speech clearly and understandably across long distances. 

These laser weapons uses a principle called the Laser Induced Plasma Effect, which entails the firing of an extremely powerful laser to create a ball of plasma and then shooting a second laser to oscillate the plasma, creating sound waves. During recent testing at the Naval Information Warfare Center Pacific in the USA a number of laser bursts were fired at certain frequencies through the use of an algorithm. The laser bursts were actually successful in imitating human speech through the creation of plasma vibrations.

It may sound very futuristic but according to the Pentagon in the USA, these weapons may be ready in less than five years and will enable soldiers to target specific people with messages or warnings without endangering themselves. A typical warning message with the aim of preventing death would be "stop or we will be forced to fire upon you." 

Pentagon scientist are hoping that they would eventually be able to beam messages over hundreds of kilometers via devices on the ground or on specially equipped aircraft. 

Although primarily a communication tool, talking lasers would be a powerful instrument in the control of aggressive or violent crowds over a distance. It could also be used as a method of keeping trespassers away from important installations, convoys or people. 
JNLWP scientists are simultaneously testing directed energy plasma lasers that can burn through clothing to create uncomfortable levels of skin irritation without burning the people. 

The laser-induced plasma weapon uses very high-energy lasers at a very short pulse rate to strip the electrons off a gas to create plasma. The plasma is then used to poke through clothing and drill smaller than microscopic holes in the skin of the person. The drilling does not cause damage but it does set off nerve responses, leading to extreme discomfort and pain.

The military is also testing plasma laser balls that generate continuous sound waves similar to the familiar stun grenades currently being used in crowd control. However, the plasma laser balls generate a continuous sound at an enormous 155 decibels (85 decibels is the threshold for hearing damage) – unlike standard stun grenades that usually only makes one loud blast to disorient people. The idea is to find ways to deter, stun, or basically stop adversaries short of killing them, as well as to control the behaviour of violent crowds.

Chinese researchers developed a laser gun akin to the laser blaster from “Star Wars.” This laser gun (the ZKZM-500) is, however, not focused on communication, but can set a target on fire at a range of 800 meters. The 15 mm caliber weapon weighs only 3 kilograms, and can fire more than 1,000 laser shots of 2 seconds each. The carbonizing beam can instantly reduce human skin and tissue to carbon.

The weapon can be fired through windows and can even burn through gas tanks and ignite anything that is flammable. And because it is silent and invisible nobody will know where the attack came from. It could easily look like an accident. Apparently the gun is not aimed at killing people and is therefore classified as non-lethal. According to a Chinese government document it is rather intended for crowd control and for setting fire to illegal banners at a protest or setting fire to the hair or clothing of protesters.

Combat will certainly change in the future with the use of talking lasers to unnerve soldiers of the enemy with secret confusing messages. And in a world currently marked by growing protests, this new non-lethal technology will most probably be used to effectively deter and control crowds. Perhaps it is time to dig up our old tin-foil helmets – but then again it was meant to stop external control of our thoughts through radio waves and not powerful laser beams that fall in the light spectrum! 

And furthermore, MIT students proved that although aluminium helmets protected the wearers from radio waves over most of the tested radio spectrum, it surprisingly amplified the 2.6 GHz and 1.2 GHz frequency bands. The 2.6 GHz is used for mobile communications and by broadcast satellites, while aeronautical radio navigation and space-to-Earth and space-to-space satellites use the 1.2 GHz band.

Modern technology may indeed alter the behaviour of crowds in the future.

Prof Louis C H Fourie is a Futurist and Technology Strategist.