The US Military Is Making Lasers That Create Voices out of Thin Air

defenseone.com ^

[BenLurkin]

The weapon is composed of two parts: first, a femtosecond laser, which shoots a burst of focused light for 10−15 seconds, just long enough to rip the electrons from air molecules and create a ball of plasma. (Sometimes called the fourth state of matter, plasma is a field of electrified gas, highly responsive to electromagnetic effects.) The scientists then hit that plasma field with a second nanolaser, tuned to an extremely narrow range of wavelengths. They use that to manipulate the plasma field in a way that can produce light and noise. Get the interaction precise enough and you get something that sounds like a haunted walkie-talkie.

...

The weapon’s most interesting aspect may be the way it creates noise: at a specific and distant point in space, rather than blasting it out of a nearby speaker. That means that soldiers between the weapon and the target are unaffected.

How far away can that point be? “Range is a function of the optics. The bigger the mirrors, the farther the range,” Law said. A five-inch mirror creates the effect about one kilometer away; an 8-inch mirror, about five kilometers, he said. “They’ve created plasmas at 20 or 30 kilometers,” he said. “This is the first non-lethal weapon that could go out tens of kilometers.” The Kerr effect, a term that refers to minute changes in the refractive index as a result of electromagnetic field changes, makes it actually easier to create the effect at a distance.

“One of the things about the ultra short pulse, it wants to form at longer ranges. It’s harder to form at shorter ranges,” said Law.

[DiogenesLamp]

I remember back in the 70’s when I sold hi-fi there were articles about attempting to produce sound “in thin air” without a physical driver.

I figured out how to do that in theory several decades ago. Heterodyning two High frequency audio signals (above the range of human hearing) with a differential frequency of what you want the sound to be.

Focus the two sources at a point in space, and you can create compressions and rarefactions that correspond to the audio signal you wish to reproduce.

I've read that people have actually done this, and I pat myself on the back for having thought of how to do it in theory back in the 1980s.

But doing it with light will give you a far greater range, because you have more control with light than you would with high frequency audio signals.

[daniel1212]

Like rail guns and hypersonic vehicles which should have been kept secret (if that is still possible) rather than advertised to incite Putin and the Chinese to develop the same, this also, if of any significance, should not be reported on.