Superpolishing

Superpolishing

Illustration above show the surface polish levels as measured by an optical profilometer and Nomarski microscope of actual superpolished surfaces.  Measurement were made utilizing REO metrology equipment which enables us to produce some of the smoothest surfaces in the world using proprietary materials and processes developed through years of research and manufacturing production. “Superpolishing” refers to processes that are designed to produce surfaces featuring exceptionally low scattering of light in the UV to IR wavelength ranges. These superpolished surfaces often demonstrate surface scattering levels lower than 1ppm (wavelength dependent). In terms of surface roughness, this typically means surfaces with significantly less than 1A rms, integrated over spatial scales from approximately 1 micron to 100 microns. Superpolished surfaces may be flat or spherical with a radius of curvature as short as 20mm.

Superpolished surfaces are generally characterized using optical profilometry techniques which are sensitive across the applicable spatial scale. Other techniques such as atomic force microscopy and stylus profilometry may also be used but generally perform best outside of the spatial range generally relating to optical scatter. When coated with a highly reflective coating, the total loss of a surface may be measured with high sensitivity using a cavity ring down technique.

Superpolishing does not relate directly to surface quality, which typically refers to the control of localized defects, such as scratches, digs, coating defects, and certain types of contamination. However, the techniques used to achieve a superpolished surface generally also produce a surface of high surface quality, or low defect levels.

REO produces surfaces with less than 0.3A rms surface roughness over the 1um to 100um spatial range in a number of optically important materials such as fused silica, zerodur, and BK7 glass. Mirrors comprised of such surfaces and smooth IBS high reflecting coatings can achieve total optical scatter levels of significantly less than 1ppm and total loss values less than just a few ppm in the visible and near infrared.

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