Electron micrograph of an array of gold antennas on a silicon surface. The array is created by repeating the sequence in yellow across the entire surface. Each antenna has a thickness of 50 nanometers (50 billionths of a meter). The scale bar is in microns, its length slightly shorter than a ten-thousandth of an inch. Image courtesy of Nanfang Yu.
An array of nanoscale resonators, much thinner than a wavelength, creates a constant gradient across the surface of the silicon. In this visualization, the light ray hits the surface perpendicularly, from below. The resonators on the left hold the energy slightly longer than those on the right, so the wavefront (red line) propagates at an angle. Without the array, it would be parallel to the surface. Image courtesy of Nanfang Yu.
06 September 2011
Exploiting a novel technique called phase discontinuity, researchers at the Harvard School of Engineering and Applied Sciences (SEAS) have induced light rays to behave in a way that defies the centuries-old laws of reflection and refraction.
"By incorporating a gradient of phase discontinuities across the interface, the laws of reflection and refraction become designer laws, and a panoply of new phenomena appear," says Zeno Gaburro, a visiting scholar in Capasso's group who was co-principal investigator for this work. "The reflected beam can bounce backward instead of forward. You can create negative refraction. There is a new angle of total internal reflection."
Moreover, the frequency (color), amplitude (brightness), and polarization of the light can also be controlled, meaning that the output is in essence a designer beam.
The researchers have already succeeded at producing a vortex beam (a helical, corkscrew-shaped stream of light) from a flat surface. They also envision flat lenses that could focus an image without aberrations.