Michael Kuchel

TL;DR: In this article, a test optic is aligned and moved with respect to a scanning axis relative to the origin of a known spherical wavefront that is generated with a reference surface to intersect the test optic at the apex of the aspherical surface and at radial zones where the spherical wave front and the aspheric surface possess common tangents.

TL;DR: In this paper, the authors present a method that uses the inherent symmetry of the problem to scan along the optical axis, gathering measurements at zones of normal discrepancy, which are independent from each other; their ensemble represents directly the surface deviation in normal direction to the surface and the result is in the object coordinates of the design surface.

Abstract: Interferometric scanning method(s) and apparatus for measuring test optics having aspherical surfaces including those with large departures from spherical. A reference wavefront is generated from a known origin along a scanning axis. A test optic is aligned on the scanning axis and selectively moved along it relative to the known origin so that the reference wavefront intersects the test optic at the apex of the aspherical surface and at one or more radial positions where the reference wavefront and the aspheric surface intersect at points of common tangency (“zones”) to generate interferograms containing phase information about the differences in optical path length between the center of the test optic and the one or more radial positions. The interferograms are imaged onto a detector to provide an electronic signal carrying the phase information. The axial distance, ν, by which the test optic is moved with respect to the origin is interferometrically measured, and the detector pixel height corresponding to where the reference wavefront and test surface slopes match for each scan position is determined. The angles, α, of the actual normal to the surface of points Q at each “zone” are determined against the scan or z-axis. Using the angles, α, the coordinates z and h of the aspheric surface are determined at common points of tangency and at their vicinity with α min ≦α≦α max , where α min and α max correspond to detector pixels heights where the fringe density in the interferogram is still low. The results can be reported as a departure from the design or in absolute terms.

TL;DR: In this article, a traceable calibration method was proposed to reduce the uncertainty in the precision measurement of aspheric surfaces and wavefronts by using a sliding-way approach.

TL;DR: In this paper, the authors extend and improve the basic technique of phase shifting interferometry by minimizing the measurement errors introduced by additional unwanted reflections from surfaces and surface defects far from the surface of interest.