The Stark shift due to blackbody radiation (BBR) is the key factor limiting the performance of many atomic frequency standards, with the BBR environment inside the clock apparatus being difficult to characterize at a high level of precision. Here we demonstrate an in-vacuum radiation shield that furnishes a uniform, well-characterized BBR environment for the atoms in an ytterbium optical lattice clock. Operated at room temperature, this shield enables specification of the BBR environment to a corresponding fractional clock uncertainty contribution of 5.5 × 10 −19 . Combined with uncertainty in the atomic response, the total uncertainty of the BBR Stark shift is now 1×10 −18 . Further operation of the shield at elevated temperatures enables a direct measure of the BBR shift temperature dependence and demonstrates consistency between our evaluated BBR environment and the expected atomic response.

Vertically aligned multiwall carbon nanotubes were grown by water-assisted chemical vapor deposition on a large-area lithium tantalate pyroelectric detector. The processing parameters are nominally identical to those by which others have achieved the "world's darkest substance" on a silicon substrate. The pyroelectric detector material, though a good candidate for such a coating, presents additional challenges and outcomes. After coating, a cycle of heating, electric field poling, and cooling was employed to restore the spontaneous polarization perpendicular to the detector electrodes. The detector responsivity is reported along with imaging as well as visible and infrared reflectance measurements of the detector and a silicon witness sample. We find that the detector responsivity is slightly compromised by the heat of processing and the coating properties are substrate dependent. However, it is possible to achieve nearly ideal values of detector reflectance uniformly less than 0.1% from 400 nm to 4 microm and less than 1% from 4 to 14 microm.

An integrating-sphere system has been designed and constructed for multiple optical properties measurement in the IR spectral range. In particular, for specular samples, the absolute transmittance and reflectance can be measured directly with high accuracy and the absorptance can be obtained from these by simple calculation. These properties are measured with a Fourier transform spectrophotometer for several samples of both opaque and transmitting materials. The expanded uncertainties of the measurements are shown to be less than 0.003 (absolute) over most of the detector-limited working spectral range of 2 to 18 microm. The sphere is manipulated by means of two rotation stages that enable the ports on the sphere to be rearranged in any orientation relative to the input beam. Although the sphere system is used for infrared spectral measurements, the measurement method, design principles, and features are generally applicable to other wavelengths as well.

SUMMARY In large‐scale fires, the input of energy to burning materials occurs predominantly by radiative transfer. The in‐depth (rather than just surface) absorption of radiant energy by a polymer influences its ignition time and burning rate. The present investigation examines two methods for obtaining the absorption coefficient of polymers for infrared radiation from high‐temperature sources: a broadband method and a spectral method. Data on the total average broadband transmittance for 11 thermoplastics are presented (as are reflectance data), and the absorption coefficient is found to vary with thickness. Implications for modeling of mass loss experiments are discussed. Copyright © 2011 John Wiley & Sons, Ltd.

This article reports the first comprehensive results obtained from a fully functional, recently established infrared spectral-emissivity measurement facility at the National Institute of Standards and Technology (NIST). First, sample surface temperatures are obtained with a radiometer using actual emittance values from a newly designed sphere reflectometer and a comparison between the radiometer temperatures and contact thermometry results is presented. Spectral emissivity measurements are made by comparison of the sample spectral radiance to that of a reference blackbody at a similar (but not identical) temperature. Initial materials selected for measurement are potential candidates for use as spectral emissivity standards or are of particular technical interest. Temperature-resolved measurements of the spectral directional emissivity of SiC and Pt-10Rh are performed in the spectral range of 2-20 µm, over a temperature range from 300 to 900 • C at normal incidence.Further, a careful study of the uncertainty components of this measurement is presented.

The sections in this article are Introduction Terminology Historical Review Theory of Sphere Throughput Reflectance Techniques Absolute Reflectance Methods Relative Reflectance Methods Dealing with Error Sources: Sphere Design Considerations Detector Field of View and Sphere Symmetry Baffle Design Coating and Sample BRDF Flat versus Curved Samples Port Design Modern Sphere Instrumentation for Spectroscopy Summary and Discussion Disclaimer Appendix

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We experimentally demonstrate a nearly wavelength-independent optical reflection from an extremely rough carbon nanotube sample. The sample is made of a vertically aligned nanotube array, is a super dark material, and exhibits a near-perfect blackbody emission at T=450 K-600 K. No other material exhibits such optical properties, i.e., ultralow reflectance accompanied by a lack of wavelength scaling behavior. This observation is a result of the lowest ever measured reflectance (R=0.0003) of the sample over a broad infrared wavelength of 3 μm < λ < 13 μm. This discovery may be attributed to the unique interlocking surface of the nanotube array, consisting of both a global, large scale and a short-range randomness.