Interferometric measurement of near-cylindrical surfaces with high amplitude resolution

Abstract

Subaperture interferometric measurements of highly curved surfaces with a shape close to a cylinder have been performed in a normal-incident setup that consists of a Fizeau interferometer in combination with a plano-concave cylindrical lens. Since the field of view in the circumferential direction is limited by spherical aberration, the optical components were designed to minimize spherical aberration. For reference measurements a second plano-convex cylindrical lens was used. The subaperture setup leads to three-dimensional surface maps of the objects under test. To eliminate the influence of residual geometric aberrations, rectangular polynomials have been fitted and subtracted from the raw data. For deformations with spatial wavelengths below 30 mm, a rms amplitude resolution of 1 nm and a rms amplitude accuracy of 3 nm were achieved. Measurements on Wolter-type-I mirror shells are discussed in detail.

<title>Assembly, performance prediction, and x-ray test of the optical demonstration model (ODM) for the x-ray telescope XMM</title>

“…6 displayes the computed scatter plots in an intrafocal plane, 100 mm from the nominal focal plane, for a typical mirror with only one (left side) and both Monte-Carlo processes (right side). It turns out that the quadratic summation of the HEW contributions give results for the overall HEW S close to the results of the two-step Monte Carlo simulations: s2=s?+s=s?+(2v1.35r)2 (5) The factor 2 accounts for the angle of deflection being twice as large as the surface slope error;…”