Exotic optical properties seen in the left glass, filled with negative refractive index water (Photo: Stanford University)
Electric field response of the conformally mapped nanocrescents used in the Stanford metamaterial (Photo: Stanford University)
The Stanford metamaterial shows negative refractive index over a broad band of optical wavelengths (Photo: Stanford University)
A Stanford breakthrough in optical metamaterials could enable fabrication of a wide-spectrum invisibility cloak (Image: Shutterstock)
A prism made of the Stanford metamaterial shows negative refractive index by refracting a beam of light backwards compared to how a normal prism would (blue line) (Photo: Stanford University)
An invisibility cloak works by bending light around a central region (Image: Brian Dodson)
To make a Harry Potter-style invisibility cloak requires that the materials from which it is made have a negative refractive index over all optical wavelengths, from red to violet. However, the artificially-structured optical materials from which cloaks are made thus far have been restricted to a very narrow range of optical wavelengths, limiting their ability to cloak over a range of colors. That obstacle to progress ends now, as a group of Stanford optical engineers at Stanford has succeeded in designing a broadband metamaterial that exhibits a negative refractive index over nearly the entire rainbow.
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