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20 Jun 2002
Researchers in the Netherlands have found that polystyrene is almost invisible to terahertz waves.
Polystyrene foam has dielectric properties that make it an ideal material for use in imaging devices based on terahertz radiation, according to Dutch scientists.
A series of measurements performed by researchers from Delft University of Technology show that polystyrene offers a very low refractive index (around 1.016 to 1.022) and little dispersion in the 0.1 to 4 THz region. As a result, pulses of terahertz radiation pass through the material will almost no loss or distortion.
Research groups all around the world are currently developing terahertz imagers that operate in this spectral region to penetrate fog, detect explosives and probe the inner workings of biological samples.
However, work is being hampered by the lack of suitable materials that offer a low refractive index and are highly transparent in the terahertz frequency range.
The Delft team says that polysterene is well suited as both a substrate material for terahertz imagers and a filter material for blocking near-infrared light while passing terahertz pulses.
The team performed transmission experiments with three types of polystyrene made with various blowing agents. Samples just 2 cm thick were placed in the path of the terahertz waves and their extinction coefficient and refractive index were plotted against frequency. Polystyrene blown with carbon-dioxide performed best in the experiments.
Author
Oliver Graydon is editor of Opto and Laser Europe magazine.
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