May 31, 2009 Scientists have for the first time devised a multi-pixel modulator for light waves at terahertz (THz, or 1012 Hz) frequencies. The formal study of THz radiation, which can be described as far-infrared light, dates back many years, but has become increasingly widespread since around 1990, when efficient methods for generating and detecting the radiation become available. The expected applications include carrying out biological spectroscopy and imaging buried structures in semiconductors.
Rice University physicist Daniel Mittleman and his colleagues at Sandia and Los Alamos National Labs use a metamaterial to turn a stream of THz waves off and on. It's called a metamaterial since it consists of an array of microscopic split metal rings. The rings can be controlled by nearby electrodes; modulating the ring's capacitance, in turn, modulates the radiation; that is, the THz light (sometimes called T rays) can be switched so as to pass through or not. The modulator consists of 16 pixels in a 4 x 4 array.
Mittleman reports that this is the first time the wavefront of a THz beam has been under electrical control, which is important because THz wavelengths may be good for imaging and this would be the first step in allowing that by sending light across a whole plane, not just as a linear burst. The switching speed, about 1 MHz, isn't fast compared to today's quickest data transmissions. But, Mittleman say, high bandwidth is not necessary for many of the imaging tasks that will be carried out by T rays. A larger 32 x 32 pixel array is now being designed.
This research is scheduled to be presented during the 2009 Conference on Lasers and Electro-Optics/International Quantum Electronics Conference (CLEO/IQEC) May 31 to June 5 at the Baltimore Convention Center in Baltimore.
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