The Jet Fighter Laser Cannon

fahrbot-bot sends in a Register piece about DARPA issuing the penultimate contract for what is intended to be a jet-mounted laser cannon. The Reg outdoes itself in a BOTEC involving downsizing to shark scale. "The US military will shortly issue a brace of contracts for 'refrigerator sized' laser blaster cannons. One of the deals will see a full-power ground prototype built which will be the final stage prior to America's first raygun-equipped jet fighter. ... If it scales down far enough, this would seem to put handheld HELL-guns within an order of magnitude of the striking power offered by conventional small-arms. A 9mm pistol bullet has about 750 joules muzzle energy: a 5kg portable HELL-ray weapon would put out this much energy in a blast less than a second long. ... A dolphin can carry a human being weighing up to 100kg along for a ride. A thoroughbred shark in good training can surely match this. Thus, we seem to be looking at practicable head-[laser] output in the 20-kilowatt range."

Comments

Re:9mm?

[Shakrai]

Yeah, the Air Marshals use the .357 SIG, as does the Secret Service. The Coast Guard adopted it as well. I believe the FBI is still using the .40 S&W but I could be mistaken.

The 9mm is a joke. It's even worse for the military because they aren't allowed to use expanding ammunition. Buddy of mine who deployed in Iraq tells a story of an insurgent whom wasn't stopped in spite of the fact that he had absorbed no less than six center of mass hits from the M9. Makes you question the wisdom of the military abandoning the Model 1911, doesn't it?

Re:Effect on humans?

[smellsofbikes]

I can tell you from personal experience that high power lasers cause cauterized burns (in fact, if it's a big enough UV laser you get to watch your skin glow briefly: everything fluoresces and phosphoresces if you hit it with enough photons, I think) and causes blindness. Weird corollary: visible lasers are the nasty ones because they blow holes in the back of your eye, where we can't fix things. Most of the visible-wavelength laser PhD's I've worked with have had partial blindness in some area because they've cooked their retinas. However, IR and UV lasers, while seemingly more dangerous (because you can't see them and don't know you're being hit until it hurts/your vision goes fuzzy) are actually nicer since they primarily bake the front part of the eye, and we can repair that, either with corneal transplants or new intraocular lens implants. One of the PhD's I was working with on a massive UV laser had given himself DIY laser keratotomy: he'd flattened one cornea when a laser discharged a single pulse while his right eye was in the beampath. (It was one hell of a laser: we'd warm it up in the morning using a brick, because they're cheap and *anything* in front of a kilowatt laser is disposable so you might as well go with cheap.)

The fluorescence/phosphorescence was the most interesting thing to me. They're the same effect but different phenomena: you hit something really hard with a bunch of UV, and the surface -- the stuff that didn't get ablated -- is now covered in molecules with electrons blown up into higher orbitals. The ones that fall down immediately (within nanoseconds) are what produce fluorescence. The ones that have absorbed enough energy that they're in an orbital/spin combination that won't allow them to directly drop down to their original orbital, take a long time before they can do something like electron tunnelling to return to their orbital -- where by 'long time' I mean from a millisecond up to maybe six hours. So that's where you get actual glow-in-the-dark. I could put a notecard up in the beam and trigger a shot, and there'd be a nice yellow glow off the piece of paper for maybe half a second, and then the paper itself would be a moderate brown color. Next shot and it'd be gone. The individual shots were on the order of a microsecond long.

Interesting factoid that I wish I didn't know: fluorine gas smells somewhat like Elmer's Glue. Deep UV lasers often use fluorine as an excimer and when you have to replace the cavity mirrors, no matter how many times you purge it with argon, there's still some fluorine in there when you finally open it up. Gack *cough*.

Re:9mm?

[KibibyteBrain]

All it would have to do is heat up the fuel tanks to combustion. It may not even have to do that, the thermals on jet fighter engines are insane. The exhaust leaves at far greater than the melting temperature of the alloy the engines are made out of. Therefore all sorts of tricks like laminar airflow cooling are used. However, an external source of heat into the system could totally mess up those cooling techniques...