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  1. Science & Tech
9 July 2014updated 09 Jun 2021 11:16am

Light scanners are set to get rid of that annoying ban on liquids on planes

An Oxfordshire-based company has developed hi-tech scanners which can rapidly analyse the chemical make-up of liquids inside containers.

By Ajit Niranjan

There are few places more stressful than the airport. There’s the constant queuing, the twice-hourly checks that your passport hasn’t vanished stepping from the shuttle-bus to WH Smith, and then the extra 3kg of jumpers you’re wearing because they didn’t make it through Ryanair’s paltry baggage allowance. Finally you make it to the security desk. You’re not a terrorist, so this should be a breeze, right? Wrong, you think, as you join the crowd of tourists tossing perfectly usable bottles of shampoo, water and other innocuous substances into a big plastic bin bag.

For those who’ve ever felt the 100ml ban on liquids and the see-through bags for each of your toiletries is overkill, you might be in luck. Amid mounting pressure from America to beef up airport security checks, a company in Oxfordshire has been working on a solution to bypassing strict liquid limits. They’ve created an advanced scanner capable of quickly assessing substances for chemical threats – without even opening the bottles.

The scanner, developed by Cobalt Light Systems, uses a laser to obtain a “fingerprint” of the chemicals inside the container. It’s an emerging technology called Spatially Offset Raman Spectroscopy (SORS), which relies on “monochromatic light scattering of red-shifted photons”. To understand how this complex chemical analysis technique works, we first need to ask a more basic question – why is the sky blue?

When sunlight passes through the air, tiny packets of energy – photons – are scattered by gas molecules in the air. This “white” light is actually composed of every colour of the rainbow. Blue, because of its shorter wavelength, scatters more easily than the others, so when we look up at the sky this is most of what we see. The process is called elastic scattering, which means the energy levels of the photons remain constant. As the sun sets, the angle at which sunlight hits the atmosphere changes relative to your own position on the Earth’s surface, shifting the spectrum of scattered light from blue through towards red.

Raman scattering, which is inelastic, is a little different to this. A tiny fraction of the scattered light – a miniscule 1 in 30 million photons – will interact with the liquid and gas molecules, losing a bit of its energy and vibrating at a lower frequency than before. A detector can measure the change in vibrations of these photons and produce a unique line spectrum, which provides specific information about the molecules present. This “energy fingerprint” then gets checked against a vast database of line spectra for potentially threatening chemicals. If you can make a bomb out of it, it won’t get through.

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The technique isn’t really anything new – the Nobel Prize winning physicist CV Raman first discovered the phenomenon of inelastic light scattering as early as the 1920s – but until recently it could only be used on a surface layers. SORS scanners are a variation of Raman’s which allow for deeper penetration beneath the obscuring layers, including opaque containers. Cobalt’s vice president Ken Mann claims their scanner “can go through virtually all containers you could come up against, to actually tell you what’s on the other side of the barrier.”

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So what does this mean for airports? Cobalt’s scanner is already in 65 European airports, including Heathrow and Gatwick, where it operates alongside the 100ml limits. However, this looks set to change. The EU aims to completely lift the ban by 2016 and simply scan all liquid, aerosols and gels for chemically hazardous substances. Officials hope the speed and accuracy of SORS will make it ubiquitous.

It’s all promising stuff. Just last week Cobalt won the prestigious Macrobert Award – the Royal Academy of Engineering’s highest accolade for innovation – for their laser technology, which has a diverse array of applications. Raman spectroscopy is being trialled for non-invasive cancer screenings and has already been used to detect counterfeit pharmaceuticals without removing them from their packets – all of this in addition to its security capabilities in aviation.