We present directional hemispherical reflectance (DHR) and bidirectional reflectance distribution function (BRDF) measurements of a carbon aerogel in the 2.5–14.3-μm infrared spectral region. The measured DHR is 1.0–1.2 ∓ 0.2% throughout the 2.5–14.3-μm infrared wavelength region. When the incidence angle is increased from 8° to 30° off normal, the DHR increases by only 0.2%; i.e., performance does not significantly degrade as a result of illumination by off-normal infrared radiation. BRDF measurements, obtained at a wavelength of 10.6 μm, indicate that carbon aerogel exhibits Lambertian behavior. The carbon aerogel’s BRDF value of 4 × 10<sup>−3</sup> sr<sup>−1</sup> is consistent with its measured DHR values. Gas adsorption and transmission-electron microscopy indicate a structure dominated by particles and pores of ≤10-nm dimension. Scanning-electron microscopy reveals surface roughness on a scale of tens of nanometers. The DHR and BRDF of carbon aerogel compare favorably with those of Martin Black and Rippey, two widely used nonreflective materials.
© 2000 Optical Society of America
(160.2750) Materials : Glass and other amorphous materials
(160.4670) Materials : Optical materials
(160.4760) Materials : Optical properties
(290.5820) Scattering : Scattering measurements
(290.5880) Scattering : Scattering, rough surfaces
Steven R. Meier, Michelle L. Korwin, and Celia I. Merzbacher, "Carbon Aerogel: A New Nonreflective Material for the Infrared," Appl. Opt. 39, 3940-3944 (2000)