Abstract
The absolute responsivity of a planar cryogenic radiometer fabricated from micromachined silicon and having carbon nanotubes, as the absorber and thermistor were measured in the visible and far infrared (free-field terahertz) wavelength range by means of detector-based radiometry. The temperature coefficient of the thermistor near 4.8 K and noise equivalent power were evaluated along with independent characterization of the window transmittance and specular reflectance of the nanotube absorber. Measurements of absolute power by means of electrical substitution are compared to the German national standard and the uncertainty of the radiometer responsivity as a function of wavelength is summarized.
Highlights
1.1 A brief history of the cryogenic radiometerIn the late 1800s, Samuel Langley demonstrated the first bolometer for infrared measurements [1]
One hundred years later, the electrical substitution radiometer demonstrated by Martin et al, of the National Physical Laboratory (NPL) in the United Kingdom became the definitive standard for absolute optical power measurements [3]
We extend the work of Tomlin to freefield far infrared (FIR) or terahertz (THz) radiometry
Summary
In the late 1800s, Samuel Langley demonstrated the first bolometer for infrared measurements [1]. One hundred years later, the electrical substitution radiometer demonstrated by Martin et al, of the National Physical Laboratory (NPL) in the United Kingdom became the definitive standard for absolute optical power measurements [3]. At the National Institute of Standards and Technology (NIST) more recently demonstrated that it is possible to achieve all of the essential elements of an absolute radiometer, consisting of a carbon nanotube absorber, thermistor, heater and weak thermal link; all on a microfabricated chip for optical fiber power measurements [4]. We fabricated a planar hyperblack absolute radiometer with micromachined silicon as a weak thermal link and vertically-aligned carbon nanotube arrays (VANTAs) as the absorber and thermistor. We use the term hyperblack to distinguish the fact that, rather than being hyperspectral, with multiple channels to cover a broad range of wavelengths; the nanotube-based radiometer is one detector that is nearly 100% efficient and broadly uniform over the range of 0.4 μm to 400 μm
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