For the past 15 years, scientists have been working towards creating a lens that would give people the ability to see microorganisms and nano-scale viruses with the naked eye. These “perfect lenses” would be made from metamaterials (or, materials engineered to have properties currently unobserved in nature), characterised by their unique ways of interacting with light.
Now, a team of researchers from the Michigan Technological University had just knocked down one of the biggest obstacles on the way to making the “holy grail” of optics a reality – they have managed to figure out a way how to get light waves pass through the lens without being consumed.
“These findings open the possibility of reviving the early dreams of making “magical” metamaterials from scratch,” state the researchers in their paper, published July 16 in Physical Review Letters.
The research team, led by Durdu Güney, Professor of Electrical and Computer Engineering at Michigan Tech, used thin silver films serving as the base, and tweaked them at the sub-wavelength scale so that light waves interact with the material in completely new ways.
“Aluminium and silver are the best choices so far in the visible light spectrum, not just for a perfect lens but all metamaterials,” Güney says. Metamaterials have already been made with these metals, but the problem is that they can still absorb light waves. “Loss or the undesired absorption of light is good in solar cells, but bad in a lens because it deteriorates the waves.”
For the “perfect lens” to work, it would need negative index metamaterials, as these not only pass through propagating light waves, but also amplify the decaying ones. Positive index metamaterials, on the other hand, allow only propagating light waves to pass through.
This difficulty has led researchers to try numerous modifications of the metamaterial make-up, adding bulk, mode-by-mode nit-picking and increasingly complex models. What‘s different in the present study is that Güney’s team, rather than focusing on these intricate alterations, took a step back and funnelled its energies into working with the light itself.
In their plasmon-injection scheme (shorted to pi-scheme or π-scheme), the researchers take advantage of knowing which light wave crumbles as it passes through the negative index lens. They use this wave – destined to fail in the lens – to shield the desired light wave, allowing it to pass through unscathed.
Further down the road, these improvements could lead not only to more lightweight field equipment, but also to widely accessible medical technology.
“Imaging is one of the key technologies for this work,” Güney says, adding that a perfect lens could make science and medicine real for people. “It will make life easier to understand because people will be able to see it with their own eyes.”