New advances in the design of metamaterials—specially engineered substances which have properties not found in nature—may have just overcome one of the major challenges in designing compact optical devices. The breakthrough, reported in Physical Review B, could allow scientists to study nanoscale structures using visible light: a task that was, until now, thought impossible.
Electromagnetic radiation of any kind, whether we're talking about visible light, radio waves, or x-rays, has a specific wavelength based on its energy. The more energy a photon has, the shorter its wavelength is. This presents something of a problem, however, when trying to study things on an extremely small scale. When an object is smaller than the wavelength of the light it's illuminated with, it's very difficult to get a good picture of that object—photons can pass right through it, or bounce off at odd angles. It's a bit like trying to get a good photo of a person using a camera that picks up radio waves; you might be able to tell there's something there, but the picture would inevitably come out "fuzzy"—the photons can't be focused down onto a small enough area. This is why ultra-detailed photos of microscopic structures, like the pollen grains pictured below, often have to be taken with a special tool called a scanning electron microscope, which doesn't use light at all but rather—as the name suggests—electrons.
|Pollen grains, imaged using a Scanning Electron Microscope.|
Another way to improve an optical system's resolution is to use light of a higher energy, which has a correspondingly shorter wavelength. However, this presents problems of its own. For instance, when trying to study a biological molecule like DNA, photons of higher energy than visible light have the potential to ionize the molecule—tearing electrons loose from their atoms and influencing the molecular structure.
|Split-ring resonators can have a negative|
index of refraction, a property not found
in any natural material.
|This graphic shows the construction of a fractal Hilbert curve, built from an infinite number of self-similar, repeating shapes.|
|A graphic illustrating the new design, where a Hilbert curve-shaped|
resonator focuses microwaves down onto a detector.
Image Credit: M. Dupré, et al. Phys. Rev. B. (2016)