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Could photonics be The Force behind a real lightsaber?

As Star Wars: The Force Awakens breaks box office records worldwide, Jessica Rowbury discusses whether photonics technologies could ever be used to build a real-life lightsaber

The lightsaber, or laser sword, was first introduced to cinema goers in 1977 in Star Wars Episode IV: A New Hope as the weapon used by the Jedi and the Sith.

Although fictional, few can deny that the lightsaber is an ingenious invention. It is compact and lightweight, yet can cut through virtually anything – from metal to human flesh. On screen, lightsabers appear as glowing blades that can deflect blaster bolts and that do not pass through one another during battles.

So, with the technological advances seen in photonics, would it ever be possible to create a real-life lightsaber?

The obvious choice for building a laser sword would be to use a laser, particularly as manufacturers have been striving towards more efficient and compact machines in recent years.

One clear issue with using lasers is that, because photons are considered to be massless and incapable of interacting with each other, the beams would not clash against one another like in the Star Wars battle scenes. ‘Light doesn’t like to interact with itself, so two beams of light would actually pass through each other – which wouldn’t be very useful in a fight,’ explained physics researcher Martin Ringbauer at the University of Queensland, Australia, in a recent announcement.

However, there has been research suggesting that photons can in fact interact, and even be joined, with one another. In September, scientists from the National Institute of Standards and Technology (NIST) in the United States took a step towards building objects out of photons.

Their work builds on research from 2013, which saw Harvard and MIT scientists create photonic molecules that the team said could behave like lightsabers, with the photons pushing and deflecting each other but staying linked.

To do this, the MIT/Harvard researchers pumped rubidium atoms into a vacuum chamber, and then cooled the vacuum to a few degrees above absolute zero. Weak laser light was then shone through the rubidium-filled vacuum; as individual photons travelled through the medium, they lost energy to the rubidium atoms, slowing them down. When the researchers used the laser to fire two photons, instead of one, they found that the photons became a two-photon molecule by the time it left the medium.

By tweaking a few parameters of MIT/Harvard’s binding process, NIST scientists demonstrated that photons could travel side by side, a specific distance from each other; the arrangement is similar to the way that two hydrogen atoms sit next to each other in a hydrogen molecule.

‘We’re learning how to build complex states of light that, in turn, can be built into more complex objects. This is the first time anyone has shown how to bind two photons a finite distance apart,’ NIST’s Alexey Gorshkov said.

So, if it is possible to build a molecule of light, why not a sword?

Although the research seems to be moving in the right direction, the challenges associated with integrating a laser into a handheld weapon are numerous.

Firstly, a laser has no fixed length. One solution could be to place a small mirror at the tip of the blade, but ‘can you imagine how embarrassing it would be to show up in the battlefield with a lightsaber surrounded by a whole supporting structure for a tiny mirror at its end? Apart from being really fragile, such a blade wouldn’t be able to hurt anyone,’ wrote Gianluca Sarri, lecturer at the Queen’s University Belfast, Ireland, in an article for The Conversation.

But even if a beam of light could be controlled, the next problem is generating enough energy in the small hilt of a lightsaber to power a laser.

Thanks to better cooling techniques, safety, and improved efficiency, industrial laser systems can now reach power levels of more than 100kW. However, the power supply for these lasers is huge and would certainly not fit in the tiny hilt of a lightsaber.

In addition, just thinking about the cooling mechanism that would be needed to prevent the hilt from melting into the holder’s hand is enough to give any laser supplier a headache.

Clearly, none of these characteristics describe a lightsaber; therefore it is very unlikely that laser swords will be seen in gift shops anytime soon.

However, an alternative technology could be plasma. This material is created through a process called ionisation, whereby a gas’s atoms are stripped of its electrons, causing the plasma to glow. A neon light is an example of plasma – it consists of a tube filled with neon gas in a plasma state.

Hot plasmas emit different colours depending on the gas they consist of. This characteristic could thus be used to create the different lightsabers seen in the Star Wars films; chlorine plasma, which emits green light, could yield the green weapons used by the Jedi, while the red lightsabers of the Sith could be created using helium, which emits in the red-to-violet region of the spectrum.

And because plasma conducts electricity, it can transport large electrical currents to the target material, causing it to heat up and melt. As stated in Sarri's article, in theory, a small but powerful power supply integrated into the hilt could be attached to a long, tiny filament that carries the electrical discharge and circulates gas around it. When the electrical current is turned on, the filament would become incandescent and the gas around it would turn into colourful, glowing plasma.

Don Lincoln, senior scientist from the United States’ Fermi National Accelerator Laboratory, calculated the energy a lightsaber would need to melt a blast door, which he described in an article on Space.com. Lincoln watched a sequence from Star Wars Episode I: The Phantom Menace showing Qui-Gon Jinn cutting through a heavy blast door – so, by assuming that the door was made of steel, and measuring the time it took, he estimated that 20MW of power would be required. This is enough power to run 14,000 average American houses.

Clearly, a power source of that density is beyond current technology. In addition, those sorts of temperatures would not only melt the door, but the Jedi’s hands. ‘So some sort of force field must keep in the heat,’ Lincoln said in the article. But ‘the blades appear to be using optical wavelengths, so the force field must contain infrared radiation, but let visible light through,’ he added.

‘Such technical investigations lead inevitably to invocations of unknown technologies. But, once you've done that, it is easy to simply say that the lightsaber consists of some kind of concentrated energy stored in a force field,’ Lincoln wrote.

So, how likely is it that a real-life lightsaber will ever be built? Although it seems obvious that they won’t be found in shops in time for next Christmas, the answer seems more complex than a simple ‘no’.