Invisibility at the flick of a switch
he powerful ‘Optical parametric generator’ laser we use for these experiments. It uses special optical crystals we get from collaborating Russian scientists and it produces peak powers approaching 10 million watts.
Dr Mark Frogley and Professor Chris Phillips - Imperial College London
Adverts for x-ray specs have tantalised kids throughout the decades. Sadly the reality is always a pair of useless plastic glasses, but this could all change due to a breakthrough made at Imperial College London. By exploiting the way that atoms move in solids the researchers have made solid materials turn completely transparent. 'This real-life x-ray specs effect relies on a property of matter that is usually ignored that the electrons it contains move in a wave-like way', says Chris Phillips. 'What we have learnt is how to control these waves directly'.
The secret to this breakthrough at Imperial College London is specially patterned crystals made up of nanoscale boxes that hold electrons. 'Basically we have made 'designer atoms'', says Chris. 'By choosing the size and shape of our little boxes, we can use the rules of quantum mechanics to choose the energy levels of the electrons that are trapped inside them'. When light is shone on these crystals it becomes entangled at a molecular level rather than being absorbed, causing the material to become transparent. 'You can think of the effect as similar to the way that the peaks and troughs of water waves cancel each other out to create calm water', explains Mark Frogley. 'In the materials created it is the wave patterns of the electrons that cancel each other allowing light to travel through the material and making it transparent'. At the moment the effect can only be produced in a lab under specific conditions but future applications could include seeing through rubble at earthquake sites, or looking at parts of the body obscured by bone.
Despite the almost magical feat of making solids transparent the key finding of this research is the fundamental physical effect creating the transparency. This effect has potential in the development of new efficient lasers, data security and quantum computing.
A stumbling block for the development of lasers has always been the need to create something called population inversion in the material that amplifies the light, normally glass or crystal. 'Einstein showed that, to make lasers, you need to excite the molecules into this population inversion condition, where they no longer absorb light', explains Mark. The breakthrough at Imperial College London demonstrates that light can now be amplified without the need to create population inversion. This contradicts Einstein's long-standing rule, and opens up the way for the development of a whole new range of lasers.
Data security could be improved due to the discovery that as light passes through these crystals it slows right down and could potentially be stopped and stored. Chris explains, 'When we send information as light pulses down optical fibres, it can only be accessed by making a form of measurement, which disturbs the information. This technology means we could send light signals through a network without having to disturb them ourselves. So, if confidential information was being spied on, the disturbance would show up and we could nab the eavesdropper with 100% certainty'.