beryllium coating, electron micrographs, etching, baffle materials


Beryllium coatings with varying thicknesses and columnar grain sizes were deposited by low temperature magnetron sputtering and wet chemically etched to enhance diffuse absorption of light. After etching these coatings exhibited a matte black surface finish and low specular reflectance (below 2%) in the IR up to a critical wavelength dependent upon the original grain size of the coating. Extremely thick coatings (350 µm) with original grain sizes of 10 to 12 µm were produced which exhibited specular reflectances below 0.5% up to 50 µm wavelength and a Lambertian BRDF at 10.6 µm averaging 4.3x10-3 ster-1. Scanning electron micrographs are presented for etched and unetched beryllium coatings which showed the etching process produces roughness and porosity over several size scales simultaneously with the maximum size scale limited by the initial coating grain size and thickness. This technique for producing diffuse absorbing baffle materials has great versatility in choice of coating material and substrate and can be expected to provide optical system designers with a variety of material options for stray light management.

Original Publication Citation

C.M. Egert and D.D. Allred, "Light Absorbing Beryllium Coating Produced by Magnetron Sputtering," Stray Light in Optical Systems, Robert P. Breault, Editor, Proceedings of SPIE 1331, 17-178 (199).

Document Type

Peer-Reviewed Article

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Permanent URL


Society of Photo Optical Instrumentation Engineers (SPIE)




Physical and Mathematical Sciences


Physics and Astronomy