Seeing through physics

Anglo-Swiss nanotech research paves the way for lasers that could make solid materials ‘transparent’.


Childhood fantasies of seeing through brick walls and closed doors could be a step closer to reality following work by researchers from Imperial College London and the University of Neuchatel, Switzerland.

They have developed a technique that, under laboratory conditions, makes solid objects appear transparent. The effect exploits the way electrons move in matter.


Overturning Einstein

Normally, when light is shone on to a material, the light’s energy is absorbed by its electrons. However, using a new material created from nanoscale crystals, an ‘X-ray effect’ has been achieved by shining a laser on to the structure to ‘control’ the ‘wave-like’ character of the electrons in such a way that they interfere with one another. The material then ceases to absorb light, becoming transparent in the process.

The work is based on a breakthrough that contradicts Einstein’s theory that for a laser to work, the light-amplifying material it contains, usually a crystal or glass, must be brought to a state known as ‘population inversion’.

This refers to the condition of the atoms within the material, which must be excited with enough energy to make them emit rather than absorb light.

But because the new transparent material created by the entanglement of light is made up of molecules that are half matter and half light, light can now be amplified by the material without this population inversion — the first time the effect has been seen in a solid.

Unfortunately, this process is currently invisible to the naked eye, but Imperial researcher Prof Chris Phillips explained: ‘Shining a laser light at my hand at a wavelength you cannot see would open up a transparent window and you’d be able to see right through my hand.’

Potential applications for such a breakthrough are extensive. It could, for example, be used at earthquake sites to locate those trapped under rubble. Alternatively, the researchers envisage medical uses such as examining body parts obscured by bone.


Proof of the principle

At the moment the technology is restricted to the lab, but, according to Phillips, that’s not to say it cannot happen.

‘Seeing through walls and bodies is exciting and possible but a long way off,’ he said. ‘We have proved the principle. For wider applications we’d need a rather cleverer laser than the one we’ve got at the moment. But this is a technological barrier, rather than a fundamental one.’

Phillips hopes that in the first instance the new technology will enable lasers to be developed with a much higher power and far wider range of wavelengths than can be achieved at the moment.

The three-year joint research project with the University of Neuchatel was funded by an EPSRC grant of just over £600,000.