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February 28, 2019 07:00 am

Scientists Luck Upon a New Way To Make a Rainbow

sciencehabit shares a report from Science Magazine: Chemists have stumbled across a new way to separate reflected light into the colors of the rainbow -- a phenomenon known as iridescence. The surprisingly simple technique, which is something of a hybrid of previously known ones, could have applications both scientific and aesthetic. In iridescence, an object reflects different colors at different angles, separating white light into its constituent colors. Now, [researchers] at Pennsylvania State University in State College report producing iridescence in a new way. They happened across the effect in early 2017, when they cooked up micron-size spherical droplets containing two types of oil in which the lighter oil formed a lentil-shaped upper layer the researchers hoped to use as a lens. But surprisingly, when illuminated from above, the edges of the lentils glowed with a color that depended on their size and the angle at which they were viewed, the team reports today in Nature. Clarity came only with the computer simulations performed [the researchers]. Their analysis showed the iridescence emerges through a new mechanism that blends certain elements of the previously known ones. [...] Engineers already use thin-films and refractive particles to create iridescence in video displays, paints, and decorative wall coverings. With its simplicity and adjustability, the new effect could open ways to color the world. The effect can be explained in a much simpler system: "water droplets that condense and hang from the underside of the lid of a petri dish. Light waves entering near one edge of a droplet can bounce two or more times off the dome of the droplet before emerging near the other edge -- much as light reflects off the back of a raindrop in a rainbow. However, the light waves entering at slightly different distances from the center of the droplet can bounce different numbers of times. And waves bouncing different numbers of times can interfere and reinforce each other, as in diffraction or thin-film interference. As a result, different colors emerge at different angles, which can be controlled by changing the size of the droplet."

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