A material with a negative index of refraction in the wavelength of light may pave the way for better communications and imaging technologies. Harnessing materials with a negative index of refraction may allow capturing images of objects that are smaller than the wavelength of visible light for research and medical imaging. The material, discovered by engineers at Purdue University (purdue.edu) consists of tiny parallel gold nanorods that conduct clouds of electrons called plasmons with a frequency of light in the near-infrared, a wavelength of 1.5 µm, the same used in fiber optic communications.

The nanorods, about 100-nm wide and 700-nm long, can reverse refraction, which occurs as electromagnetic waves bend when passing from one material into another. Refraction is caused by a change in the speed of light as it passes from one medium into another. Scientists measure this bending of radiation by its index of refraction. All natural materials, such as glass, air, and water, have positive refractive indices.

According to lead researcher Vladimir Shalaev, “The rods conduct current because they are metal, producing an effect we call optical inductance, while a material between the rods produces another effect called optical capacitance. The result is the formation of a small electromagnetic circuit, but this circuit works in higher frequencies than normal circuits, in a portion of the spectrum we call optical frequencies, which includes the near-infrared. So the structure works as kind of an optical circuit and interacts effectively with both field components of light, electrical, and magnetic.”

The research was funded by the U.S. Army Research Office and the National Science Foundation and is affiliated with Purdue's Birck Nanotechnology Center.