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A Rainbow of Possibilities

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A Rainbow of Possibilities
 An artist's representation of how a metasurface composed of nanoposts disperses light.
Credit: Ella Maru Studio

An artist's representation of how a metasurface disperses light. This metasurface—a sheet of material that can be altered on demand to exhibit properties not usually found in natural materials—was developed by Caltech's Andrei Faraon, assistant professor of applied physics and materials science; graduate student Ehsan Arbabi; and their colleagues from the Faraon lab.

When white light passes through a prism, various wavelengths are spread out, creating phenomena like the rainbow we see after a rain. Optical components known as diffraction gratings take advantage of this by using patterns in the spectra of light reflected off an object to provide information about that object's chemical makeup. Such diffraction gratings are commonly found in spectrometers.

A diagram showing how different types of lenses diffract light.
Credit: Andrei Faraon/Caltech

Just as lenses can be shaped to control how they bend light, Faraon and Arbabi demonstrated that their metasurfaces composed of nanoscale silicon pillars can be designed to perform the same task.

In a recent article published in the journal Optica, the engineers showed that the size and arrangement of these pillars can be used to control the dispersion of diffraction gratings, allowing light to be spread out over a broader range of angles or even to flip the order of the colors. 

A scanning electron microscope image of the silicon nanopillars forming a metasurface.
Credit: Andrei Faraon/Caltech

A scanning electron microscope image of the silicon nanopillars forming a metasurface, each smaller than the wavelength of light.  The team arranged them in patterns that diffract light in specific ways. This technique could be used to create future generations of spectrometers.

This discovery may yield improved performance of optical devices in applications like lasers and imaging. Faraon and Arbabi collaborated on this research with Caltech graduate students Seyedeh Mahsa Kamali, Yu Horie, and researcher Amir Arbabi. This research was funded by Samsung Electronics, the National Science Foundation, the Department of Energy, and the Defense Advanced Research Projects Agency. 


Materials engineered at the nanoscale can control the dispersion of light and could be the basis of next-generation spectrometers and other imaging devices.

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Wednesday, June 28, 2017
Noyes 147 (J. Holmes Sturdivant Lecture Hall) – Arthur Amos Noyes Laboratory of Chemical Physics

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