The team based at the National Institute of Standards and Technology (NIST) will use the new ultra-dark detector for making precision laser power measurements with applications in optical communications, laser-based manufacturing, solar energy conversion, and industrial and satellite-borne sensors. [Lehman et al., Nano Lett (2010) doi: 10.1021/nl100582j and Yang et al., Nano Lett (2008) 8 (2), 446 doi: 10.1021/nl072369t]

Recognizing the potential in 2005, NIST researchers successfully grew carbon nanotubes on a pyroelectric, but achieved 15% reflectance.[Lehman et al., Infrared Phys Technol (2006) 47, 246; doi: 10.1016/j.infrared.2004.12.004]. In 2008, scientists at the Rensselaer Polytechnic Institute then developed what they described as the darkest synthetic material ever made, which piqued the interest of the NIST team. NIST built on this earlier work with colleagues at Stony Brook University in New York and FirstNano. The SUNY researchers grew carbon nanotubes to be used as an array for coating a thermal detector. The team explains that the novel coating absorbs laser light and converts it to heat, registered in pyroelectric lithium tantalate, which produces a current correlating to the laser power. The researchers point out that the less reflective a coating on such a device, the more efficient it can be at absorbing laser light and so the more precise the measurements made with it.

The new material uniformly reflects less than 0.1% of light at wavelengths from 400-nanometre deep violet to the near infrared at 4 micrometres and less than 1% of light in the infrared spectrum from 4 to 14 micrometres. This level of “darkness” is similar to that obtained by the RPI team with their material and by researchers in Japan in 2009. The NIST work is, however, unique in that the carbon nanotubes were grown directly on to the pyroelectric material rather than silicon thus avoiding an additional step involving incorporation of a layer to indirectly convert incident laser light to a readable electrical signal.

The NIST team is now working to expand the operating range of their device by up to 100 micrometers. A device with such an increased detection range would operate at useful terahertz frequencies corresponding to the submillimetre range being investigated for medical imaging, security applications and spectroscopy as well as having manufacturing uses and potential in very high-altitude communications.