Metamaterials breakthrough could lead to the first wide-spectrum optical invisibility cloak

To make a Harry Potter-style invisibility cloak requires the use of materials that have what's known as 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 looks to be at an end, as a group of optical engineers at Stanford has succeeded in designing a broadband metamaterial that exhibits a negative refractive index over nearly the entire rainbow.