Broadband Optical Absorber

Most optically black materials rely on a textured surface or coating. The Broadband Optical Absorber is the first three-dimensional bulk optical absorber. It is based on a novel low-density carbon-carbon composite originally developed at Oak Ridge National Laboratory in Oak Ridge, Tenn., for aerospace thermal insulation applications. It is easily fabricated to net shape and is exceptionally damage resistant compared with optically black coatings.

Other optically black components rely on fine-scale surface structure formed by etching, anodizing or coating. Etched structures are effective only for wavelengths smaller than their surface features. Anodized and coated surfaces are highly vulnerable to damage. The Broadband Optical Absorber is a low-density carbon structure with large open spaces. Because its absorption is a bulk property, it is not altered by surface damage. The open space keeps spectral reflectance well under 1 percent for all wavelengths from 2 to 50 um. Scatter is isotropic with no specular component of reflection.

 

The absorber is nontoxic and less expensive than etched beryllium. It is resistant to radiation and thermal damage and can be bonded easily to graphite, metals and ceramics.

The material can be used for baffles, beam stops and other structures to protect detectors from stray light at high powers and long wavelengths. It is also useful for measurement or calibration standards for spectrophoto-meters, scatterometers or other optical instruments.