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Metamaterial prism creates a reverse rainbow

Posted January 12, 2015

In a normal rainbow, red is always on “top” while violet is on the “bottom.” This is true whether the rainbow is created by a glass prism or by water droplets in the sky, and is due to the way that these materials refract light of different wavelengths: colors with longer wavelengths (red) are less refracted/bent than colors with shorter wavelengths (violet). Now in a new study, scientists have designed a prism that does the opposite: it refracts longer wavelengths more strongly than shorter wavelengths. The result is a reverse rainbow.

 reverse rainbow
(a) Illustration of the metamaterial prism, consisting of a stack of circuit boards and metallic strips, illuminated by a horn antenna. (b) Photo of the fabricated metamaterial prism prototype. (c) Photo of the experimental setup. Credit: Morgado, et al. ©2014 AIP Publishing

The researchers, Tiago A. Morgado, et al., from the University of Coimbra, the University Institute of Lisbon, and the University of Lisbon, all in Portugal, have published their paper on creating a reverse rainbow in the microwave part of the spectrum using the new prism in a recent issue of Applied Physics Letters.

The new prism is made of metamaterials, which are man-made materials that have properties not typically found in natural materials. In this case, the atypical property is non-local topology, which gives rise to the stronger refraction of longer wavelengths and the reverse rainbow.

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