1 December 1982 Surface Roughness Measurements Of Curved Surfaces By Light Scatter
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Abstract
The use of light scatter to determine flat surface statistical information, such as a bandwidth limited section of the surface power spectral density (PSD) function and the associated rms roughness and slope numbers, is well documented in the literature. Systems which mea-sure scatter as a function of angular position often make use of the fact that the surface power spectral density function is essentially produced in the scatter pattern. Low spatial frequencies scatter close to the direc-tion of specular reflection and higher frequencies scatter further out. The technique relies on the one-to-one relationship between spatial frequen-cy and scatter position in the far field. This relationship is exact to within dimensions corresponding to the diffraction limit (i.e., dimensions much smaller than the usual detector aperture). For a curved surface, this one-to-one relationship is destroyed as scatter from a single spatial frequency can spread out to dimensions far exceeding those of a diffraction limited spot. As the spread approaches detector aperture dimensions, the ability to extract useful surface information is impaired. The amount of spread is determined by the illuminated spot radius r, the radius of curvature of the surface R, and the angle of incidence 01(r) and is plotted, for constant 01, as a function of r/R. Analytical data show that by reducing r to 0.5 mm, reasonable results are obtainable with workable scatter system geometries for curved surfaces with R _> 5 cm.
John C. Stover, "Surface Roughness Measurements Of Curved Surfaces By Light Scatter," Optical Engineering 21(6), 216987 (1 December 1982). https://doi.org/10.1117/12.7973020 . Submission:
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