A radiometer includes a substrate; a radiation absorber disposed on the substrate to absorb radiation; a thermal member disposed on the substrate to change electrical resistance in response to a change in temperature of the radiometer; and a thermal link to connect the radiometer to a thermal reference, wherein the radiation absorber, the thermal member, or a combination comprising at least one of the foregoing includes a plurality of carbon nanotubes, the carbon nanotubes being mutually aligned with respect to the substrate, and the radiometer being configured to detect optical power.
This invention is an electrical-substitution radiometer (ESR) — a thermal detector for optical and infrared radiation — based on a novel configuration of arrays of vertically aligned carbon nanotubes. An ESR is a primary reference standard used worldwide to measure optical power. It typically measures modulated optical power incident on a conical radiation-absorbing surface by sensing changes in electrical resistance caused by temperature change. The temperature change may be produced by either by optical (and infrared) absorption and heating or electrical heating. An increase in the applied heater power when the incident light is blocked is a measure of the optical power absorbed by the radiometer.
However, many ESRs can be bulky and are hand-assembled from individual components. Further, the time response of many ESRs is not optimal for detecting transient optical signatures. Moreover, some conical surfaces are not sensitive to low optical power or certain wavelengths.
The NIST ESR eliminates these limitations. It employs a novel absorber in the form of a mat containing a dense array of vertically aligned carbon nanotubes shown to absorb 99.9% of incident optical power. The nanotubes can vary in size but are often about 10 nm thick and 150 µm long. The mats are grown on a micro-machined silicon chip, an instrument design that is easy to modify and duplicate.
Scores of industries rely on various forms of radiation power measurement, and new applications arise continuously in telecommunications, laser-power measurement and many more areas. NIST’s invention solves the problem of disseminating high-accuracy and infrared measurement capability, which is beneficial for industrial, scientific and defense applications, sensing visible and infrared radiation, thermal imaging, and other sensing.