Gold Nanostructures Act as Optical Antennas

Researchers at Universität Basel in Switzerland and the Swiss Federal Institute of Technology Lausanne have constructed nanoscale structures that act as optical analogues of half-wave radio antennas. They described their findings, which may have implications in novel illumination schemes at the nanoscale level, in the June 10 issue of Science.

In the work, the scientists used focused ion-beam milling to fabricate gold rods 190 to 400 nm in length and 45 nm in width from 45-nm-thick films. They converted half of the structures into dipole antennas by cutting a 20-nm gap across the center of the rods.

Under exposure to 8-ps pulses of 830-nm radiation from a Ti:sapphire laser, the structures generated white-light supercontinuum radiation. Those with gaps displayed emissions up to 10,000 times stronger than the solid rods.

The optically resonant 255-nm-long antennas produced the greatest half-wave dipole resonance effect, despite not being a half-wavelength long. The researchers attributed this to the finite width of the structures, the effect of the ITO-coated glass substrate on which they were constructed and the low dielectric constant of gold.