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USAF seeks diamond gunports for electropulse ray-cannon

Plus: Fibre optics offer hope of shark-portable lasers

The smart choice: opportunity from uncertainty

The US Air Force has made an appeal for a range of new technologies which it will need in building its planned new arsenal of aerial rayguns. In particular, it wants large artificial optically-correct diamonds for use as portholes through which to shoot electropulse microwave blaster cannons.

Under its "Directed Energy [Weapon] Materials Program," the US Air Force Research Laboratory asked on Monday for a whole sheaf of materials miracles. The most eye-catching, we'd say, is the "High Power Microwave Windows First Category" solicitation (Word doc).

In it, the Air Force raygun boffins candidly state their desire for high-power microwave (HPM) weapons of "one megawatt or more" - in the same league power-wise as the heaviest military rayguns now in existence, and ten times the poke normally seen as essential to an entry-level laser weapon.

HPM rayguns, however, aren't intended for burning holes in stuff or people. They are intended to deliver the same sort of effects as the electromagnetic pulse (EMP) emitted by a nuclear bomb, without the need for the bucket-o-sunshine side effect and in the form of a directed beam rather than an omnidirectional zapping.

Nuke EMPs are well-known to be capable of frying or scrambling all unshielded circuitry from a substantial distance, and military electronic-warfare types have long hankered to have this sort of capability in less-drastic form.

Hence the desire for conventional HPM weapons, which have been expected in bomb format for ages. But a non-exploding raygun style of HPM is also an aspiration, and in this case, it seems that a major snag is the "window" - the gunport in the fuselage of the plane, nose of the weapons pod etc. - through which the electropulse blast is to be fired.

The windows are required not only to transmit the needed energy; they also need to be able to survive thermal transients and high electric fields without operational loss and without significant defocus of energy. Mechanical and physical properties must be adequate to provide the needed performance and survivability.

Apparently, the only stuff known to the Air Force labs which will do is "optical diamond". They want this to be cheaper, tougher, bigger and made in the US of A.

They specify that people wanting to supply pulse-blaster gunport diamonds must be able to make ones 2.5 inches across and able to withstand 11 atmospheres of pressure - as much as the lens of a cheap waterproof watch.

Another interesting requirement (Word doc) thrown out as part of the energy-weapons materials push was this one, in which the Air Force boffins express their dissatisfaction with present-day high energy lasers - proper blasters for blowing stuff up and burning holes in people. The current technology - for instance the jumbo jet nuke-nobbler laser project - uses chemically-fuelled lasers, and the limitations of these are given in some detail:

Such high power lasers suffer from... flight instability (ie vibration, moving parts), limited "shot magazine" (6-10 shot per useable "laser fuel"), long reload times (~4 minutes typically), and low laser power-to-system weight ratios (5 Watts/Lb versus desired 90 Watts/Lb*).

Even the next-gen solid state lasers - lately dubbed "the first production line energy weapons" to much fanfare - are still crap, it seems.

Second generation High Energy Laser (HEL) systems are migrating to solid state/solid host concepts such as the Joint High Power Solid State Laser (JHPSSL)... These technologies still suffer various technology problems [for instance] vibration is still a problem, beam alignment issues, pre-exit aperture free space beam propagation and, most importantly, thermal management issues.

The Air Force lab guys give it as their opinion that "ultimately, the optimal solution lies in the development of very high power fiber-based lasers and laser amplifiers". In this case, though, the Air Force Research Lab people haven't really got any idea what kind of supermaterial could be used to make the necessary fibres. Anyone who does should drop them a line.

There's more for aspiring raygun makers here (Word doc). ®

*This is presumably the maximum weight-to-power number which would allow a shark with average neck strength to deliver a fatal blast.

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