An antenna for visible light

An antenna for visible light , analogous to antennas for radio waves, can be made with carbon nanotubes (CNTs). In a process that provides the backbone of radio and TV broadcasting, a radio wave excites electrons into meaningful currents in an antenna whose length is some multiple of the wave’s half-wavelength. Scientists at Boston College used aligned but randomly placed multiwalled CNTs (see figure) as an array of little metallic antennas, each about 50 nm wide and hundreds of nanometers long, that are sensitive to optical wavelengths. The team demonstrated not only the length-matching effect, but also the disappearance of the response when the incoming light was polarized at right angles to the nanotubes’ axis. According to the team’s Zhifeng Ren, CNT optical antennas might be useful for a new generation of terahertz or infrared detectors, high-efficiency solar energy converters, or optical computers. (Y. Wang et al., Appl. Phys. Lett. 85 , 2607, 2004 http://dx.doi.org/10.1063/1.1797559 .)