Third in a series of posts inspired by ten topics in ‘Insights of the Decade’ from the December 17, 2010 special issue of Science Magazine The topics are: Inflammation, climatology, tricks of light, alien planets, the microbiome, cell development, Martian water, the DNA time machine, cosmology and epigenetics. The original articles are now behind a paywall; they won’t be reproduced here, but their gist is present. I’ll try to put them in context and specifically within the Impact Areas of SciTechStory.
In this new decade, one of the focal points of science and technology will be light. That is, light in all its daedal forms such as photons, plasmons and electromagnetic waves that are the subject of research in quantum mechanics, laser technology and transformation optics. Now most of this is not your everyday sunlight or lamplight; this is light taken down to its smallest bits (particles) or most fundamental behavior (waves). This is where light becomes, for lack of a scientific word, weird. Or less colorfully, where the properties of light become unfamiliar, unintuitive, and subject to some peculiar manipulation.
Of these manipulations of light, transformation optics is the most interesting and least known. The road to transformation optics began in 1968 with a paper by Russian physicist, Victor Veselago, who looked at standard optics – through glass – and wondered if there might be another sort of material that could defy the limitation of always bending light in a positive (greater than 1) direction. Veselago thought this would be a fine thing, to make light bend ‘backwards’ (like a straw in water only with the refraction going back toward the straw). He could visualize lenses that were flat, which could focus light better than conventional lenses.
What Veselago was wishing for (but did not himself develop) was the advent of metamaterials. Metamaterials are mostly man-made and come in many shapes and sizes, literally. Most of them fall into the category of nanomaterials – little rods, cones, spheres, and pipes only a few nanometers in size (that is, thinner than a few hundred-thousandths of a human hair). Because they are so tiny, the spaces within or formed by these metamaterials affect light in unexpected ways. In short, the spaces can be described with the mathematics of Einstein’s theory of General Relativity, where space and time are warped by gravity. In this case, it’s light or electromagnetic waves that get warped.
Late in the 1990’s John Pendry and colleagues at the Imperial College London (UK) caught on to the ability of carbon nanotubes to absorb radio waves. He went on to discover that certain nanomaterials could be ‘tuned’ to resonate with electric and magnetic fields at precise frequencies. As they resonated, they transformed the electromagnetic waves so that it was possible to create a negative refractive index (i.e. less than 1, or bend light backwards).
Pendry’s work, though controversial, could be put to the test – and many experiments in the early 2000’s started to show that indeed negative refraction was possible and shortly hyperlenses were born. By the end of the decade the experiments had gone much further, almost to the point of showing that metamaterials could bend light any way desired. For example, in 2008 Xiang Zhang and colleagues at the University of California Berkeley (USA) made three-dimensional electromagnetic waves ‘flow’ around an object – making it invisible. No, this is not a Romulan cloaking device; not yet.
Actually the ‘cloaking’ capability of transformation optics is a convenient bit of hype for properties that may have more mundane but potentially important uses. The ability to manipulate light at the wave or particle level means scientists are looking at techniques with thousands of possible applications. For example research is now looking at ways to turn electromagnetic waves that refract at half the normal wavelength of light to produce an ultra-thin high-powered laser called a spaser. [Here’s SciTechStory’s post: Progress report: Plasmon Spasers]
As scientists learn more about the behavior of light at the quantum level, they’re finding that it is not only appropriate for certain man-made applications such as electronics, but that it also exist in nature. There are already the early glimmerings of quantum-level effects with light in photosynthesis and quite possibly within the brain. (More on these topics at a later time.)
Light, the field of photonics, isn’t currently a SciTechStory impact area. It should be. The list already has 40 areas, which is itself a cut-down from many potentially important developments in science and technology. One of these days it would be great to have the readership help determine which impact areas are added (or dropped) and their relative ranking. For now though, I have to pick and choose, and it seems time to put photonics in the list.