September 14, 2006

Nanoantennas and superlens : both could focus light 20+ times better

Eric Kort and Ertugrul Cubukcu designed the optical nanoantenna to focus light from a commercial laser (with a wavelength of 830 nanometers) to a spot size of 40 nanometers. With this resolution more than three terabytes [3,000 gigabytes] worth of data could be put onto something the size of a CD.

The antenna consists of two gold-coated nano rods, separated by a 30-nanometer-wide gap, according to Crozier. When light from the laser hits the nano rods, it applies a force to the electrons in the gold, nudging them out of place. The electrons don't stay displaced for long, however, and are pulled back toward their original position. But they overshoot it, Crozier says, and bounce back out of place, oscillating "like a mass on a spring."

The nano rods and gap act as a tiny capacitor--with opposite charges on opposite sides of the gap--that effectively concentrates the energy from the laser light into a spot about the size of the gap. This spot maintains its size to about 10 nanometers away from the antenna before it starts to spread out.

It is the first time an antenna has been integrated directly onto a laser. This offers an advantage in production because the light source and antenna are in one package.

Crozier says his team is exploring fabrication techniques that can further decrease the spot size to 20 nanometers. They're also exploring alternatives to the gold metal that currently coats their nano rods. Silver, for instance, could focus light more efficiently than gold at the wavelengths used by the consumer electronics industry.

For the first time a superlens, a lens capable of creating images of objects smaller than the wavelength of light, has been integrated into a microscope and used to visualize two-dimensional objects. Shvets cautions there is much work to be done before applying the technique widely. His group at The University of Texas at Austin aims to make thinner silicon carbide films (50-100 nanometers thick) that will provide even higher resolution images.