Invisibility cloaks have drawn a step closer to realization with the development of a new material that can bend visible light — in three dimensions — in a way that naturally occurring materials cannot.
Natural materials all have a property known as a positive refractive index. But this new artificially engineered material, a so-called optical metamaterial, has a negative refractive index, which means it reflects visible light the opposite way to natural materials. If placed in water, for example, an object with a positive refractive index would appear closer to the surface than it actually is. In contrast, an object with a negative refractive index would appear farther away.
In reaching this milestone, researchers at the University of California and Lawrence Berkeley National Laboratory in Berkeley, California, crafted a multilayered ‘fishnet’ structure and showed that it unambiguously exhibits a negative refractive index in three dimensions. Previously, only thin and, effectively, two-dimensional materials had been demonstrated, limiting practical applications.
The new metamaterial can be probed easily from free space, making it functional for optical devices, according to Jason Valentine, Xiang Zhang and colleagues reporting their work in Nature this week.
This straightforward and elegant experimental demonstration of a material that can bend light the ‘wrong’ way enhances our ability to mold and harness light at will.
- Three-dimensional optical metamaterial with a negative refractive index (Letter p376, doi: 10.1038/nature07247)
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