Terahertz radiation technology is best suited for its application in package inspection, skin tumor imaging and concealed weapons detection due to its penetrating properties.
Vertically aligned carbon nanotube arrays grown on a silicon surface
Terahertz radiation can penetrate various materials such as clothing, plastic, paper and certain biological tissues. A research team from the National Institute of Standards and Technology (NIST) has developed a coating for prototype detectors which can determine terahertz laser power. It is comprised of significantly long carbon based nanotubes arranged in dense arrays which absorb almost all light of considerable length wavelengths.
The research by NIST is part of its effort to develop an initial reference standard required for calibrating lasers capable of operating in the terahertz range. The calibration is done from the far-infrared wavelength range of 100µm to the microwave band edges at 1mm.
The project leader at NIST, John Lehman stated that till date, there was no way available for measuring the absolute power for terahertz based laser sources. Vertically aligned carbon nanotube array (VANTA), the coating developed by the team seems suitable for use on terahertz laser power detectors.
The properties of VANTA (vertically aligned carbon nanotube array) include its ease of use and application. The nanotubes measure from tens of micrometers to more than a millimeter length, thus allowing visibility of the dense layer through the naked eye. A large portion of the VANTA can be sliced and transferred, allowing easy transfer from a silicon substrate to the laser power detector.
The coating is also very dark, and upon the evaluation of three samples with lengths of 40µm, 150µm and 1.5mm, researchers determined that less light is reflected by the longer tubes. This implies that the 1.5mm version of the coating practically did not reflect any light. The results indicate that since all incoming laser light will be absorbed, it would serve to determine precise measurements of laser power.
The researchers also found that heat was quickly absorbed and released by the VANTA coating as compared to other black coatings, making the detector more responsive and faster in producing signals. In enhancing the terahertz laser radiometry capability NIST is creating a terahertz laser that can perform regular measurements and a thermopile detector to determine the power of the laser.