SEDL / STP / STP911-EB / STP28976S

The Effects of Slope Error on the Imaging Quality of a Mirror as the Ratio of Surface Perturbation Depth to Wavelength Approaches Zero

Bennett, HE
Michelson Laboratory, Physics Division Naval Weapons Center, China Lake, California

Burge, DK
Michelson Laboratory, Physics Division Naval Weapons Center, China Lake, California

Pages: 5    Published: Jan 1985

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Abstract

Three parameters are needed to specify the quality of a polished mirror surface: (1) optical figure tolerance, (2) surface microroughness and scratch/dig specification, and (3) slope error. The slope error is a measure of surface ripple, i.e., long-range modulations or zones with wavelengths typically in the centimeter to tens-of-centimeters range. The increase in blur circle diameter and resulting decrease in resolution caused by slope error can normally be computed from geometrical optics, since the surface wavelength is much longer than the wavelength of incident radiation. However, as the depth of the surface perturbation becomes small compared to the optical wavelength (as may occur, for example, in going from the visible to the infrared), geometrical optics no longer applies and the effects of slope error are greatly reduced. A comparison of physical and geometrical optics calculations of the effect of slope error in this limiting case will be given.