For a quarter of a century, energy weapon enthusiasts have fantasized about a ray gun that never runs out of shots – and can be "tuned" to blast through the air, at just the right wavelength. But, for most of that time, such a "free electron laser" weapon seemed like just a dream. Now, DANGER ROOM has learned, the Navy is about to give the go-ahead to begin work on a building a battlefield-strength free electron laser. It'll take around $200 million to pull off, and it won't be ready until 2020 or so. But if it all works out as planned, military researchers may one day have "the Holy Grail of lasers" in their hands.
www.youtube.com/watch?v=OtnqJUXZLjM
Lasers all work in pretty much the same way: Excite certain kinds of atoms, and light particles — photons — radiate out. Reflect that light back into the excited atoms, and more photons appear. But unlike with a lightbulb, which glows in every direction, this second batch of photons travels only in one direction, and in a single color, or wavelength. Which slice of the spectrum depends on the “gain medium” — the type of atoms — you use to generate the beam.
These days, some lasers use use garnet crystals as their gain media. Others, huge vats of toxic chemicals. But a free electron laser (FEL) doesn't use any gain medium at all to generate its beam. It uses a turbocharged stream of electrons to kick-start its reaction, instead. And that lets the FEL fire along many different wavelengths – and for a long, long time.
The Navy is interested in the FEL because most other lasers lose strength as they move through — and get absorbed by — the atmosphere.
That's especially in moist environments; around the sea, for instance.
But the FEL can pick particular slices of the spectrum where the absorption won't be nearly as bad.
For decades, though, the problem was that no one could get the FEL the shine much stronger than a lightbulb. During the Star Wars era, the government sank ten years and a half a billion into a FEL. All it could only muster a meager 11 watts.
That changed in recent years, when researchers at the Thomas Jefferson National Accelerator Facility managed to assemble an FEL that hit 10,000 watts, or 10 kilowatts, in
2004. (The video, above, is of the Jefferson FEL in action.) The group got to 14 kilowatts two years later, and is now aiming for 20. Then, if the Navy money comes through, as is now expected, the Jefferson team will begin construction on a new FEL in 2010 designed to power up to
100 kilowatts – what's considered battlefield strength in the military world. With that much strength, an FEL could be equipped on a destroyer, zapping any incoming rockets. And a decades-long dream would be fulfilled.
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