Original URL: http://www.theregister.co.uk/2011/05/03/raygun_pointer_tech/

Boffins develop liquid crystal solid-state raygun turret

Points laser beam with no need to shift laser

By Lewis Page

Posted in Science, 3rd May 2011 15:15 GMT

OK, so you've done it. You've finally built a high-energy laser which can put out a megawatt-range beam, and it doesn't emit toxic corrosive exhaust or melt itself in operation or weigh a prohibitive amount. Now to revolutionise warfare, right?

Well, just hold on there my crazy boffin friend: it's no good trying to hold the world to ransom just yet. If you want to employ your brilliant new raygun in the most popular applications – shooting down fast-moving cannon shells or nuclear missiles in mid-air, for instance – you will need to be able to point the beam easily and quickly. Simply pointing the whole laser is unlikely to be practical: and directing a superpowered raygun beam using conventional optics such as mirrors or lenses is likely to be troublesome as even the tiniest inefficiencies could divert enough energy to make your apparatus explode.

Enter Jihwan Kim and Michael Escuti, engineering brainboxes at North Carolina State University in the USA. They say they've hit upon a means of pointing laser beams using a stack of "polarisation gratings" – liquid-crystal patterns on glass plates. These can direct even a powerful war-grade ray without getting melted themselves, apparently.

"Because each individual grating is very good at redirecting light in the desired directions with almost no absorption, the stack of gratings do not significantly weaken the laser power," says Escuti.

The doc and his colleagues write:

The device shows high optical throughput (78% −83%) that can be substantially improved by optimizing substrates and electrode materials.

The gratings are solid-state and made using normal liquid-crystal industrial methods, too, so they should be reliable, very quick-acting and low cost – just the thing for holding a powerful beam on a speeding nuclear missile (or more realistically a falling Katyusha rocket; or more realistically still holding a less powerful ray on a moving communications reception apparatus).

Though it would seem likely that the liquid-crystal beam pointer kit will actually see its first applications in such fields as sensors and comms rather than blaster cannons, it does seem promising for weapons also. The US Navy's plans for a future fleet of raygun dreadnoughts may have moved a small step further forward: and so perhaps has the glorious day of the shark-portable, hat-mounted directed energy weapon.

Kim, Escuti and their colleagues' paper Wide-angle, nonmechanical beam steering with high-throughput utilizing polarization gratings is to be published in the journal Applied Optics. Until then you can read it in PDF (12 pages/1.1MB) here. ®