Terahertz radiation can penetrate numerous materials—plastic, clothing, paper, and some biological tissues—making it an attractive candidate for applications such as concealed weapons detection, package inspection, and imaging skin tumors. However, to date there is no standard method for measuring the absolute output power of terahertz lasers, one source of this type of radiation. Now, researchers at the National Institute of Standards and Technology (NIST) have found that dense arrays of extra-long carbon nanotubes absorb nearly all light of long wavelengths, and thus are promising coatings for prototype detectors intended to measure terahertz laser power as discussed in the article, “Far infrared thermal detectors for radiometry using a carbon nanotube array,” by J .H. Lehman, B. Lee, and E. N. Grossman (Applied Optics, July 18, 2011).

The research is part of NIST’s effort to develop the first reference standards for calibrating lasers that operate in the terahertz range, from the far infrared at wavelengths of 100 micrometers to the edge of the microwave band at 1 millimeter.

“There is no measurement traceability for absolute power for terahertz laser sources,” NIST project leader John Lehman says. “We have customers asking for the calibrations. This coating looks viable for terahertz laser power detectors.”

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