Abstract: A system comprising a plurality of methods for measuring surfaces or wavefronts from a test part with greatly improved accuracy, particularly the higher spatial frequencies on aspheres. These methods involve multiple measurements of a test part. One of the methods involves calibration and control of the focusing components of a metrology gauge in order to avoid loss of resolution and accuracy when the test part is repositioned with respect to the gauge. Other methods extend conventional averaging methods for suppressing the higher spatial-frequency structure in the gauge's inherent slope-dependent inhomogeneous bias. One of these methods involve averages that suppress the part's higher spatial-frequency structure so that the gauge's bias can be disambiguated; another method directly suppresses the gauge's bias within the measurements. All of the methods can be used in conjunction in a variety of configurations that are tailored to specific geometries and tasks.

Abstract: An object fringe pattern is distinguished from other fringe patterns in an interferogram produced by an interferometer using a pair of diffraction gratings for separating and recombining test and reference beams. The object on which a test beam is grazingly incident is moved in X and Y directions in a plane perpendicular to an optical axis of the interferometer to change the brightness regions of the object fringe pattern. A computer identifies pixels whose irradiance changes in response to object movement, and then only irradiance data from the identified pixels is used in analyzing the interferogram to produce a measurement of a surface of the object.

Abstract: A Fizeau interferometer (10) producing spherical test and reference wavefronts (34 and 36) is operated with a linear translator (50) for making a sequence of subaperture measurements of an aspherical test surface (40). Separate phase maps (88 and 90) are assembled at different focus positions (54 and 56) along a common optical axis (52) of the interferometer (10) and aspherical test surface (40). Respective null zones (92 and 94) are isolated from the phase maps (88 and 90) and are combined to form a composite phase map (100) defining differences between the aspherical test surface (40) and a family of spheres.

Abstract: An interferometer (14) performs three topographical measures of an artifact (12) to determine taper between opposing surfaces (50 and 52) of the artifact (12) mounted on three points of support (30, 32, and 34). Two sets of three data points (60, 62, and 64 and 68, 70, and 72) are extracted from the first topographical measure and are used to calculate irregularities in one of the opposing surfaces (50). The second two topographical measures are made of the other artifact surface (52). Taper between the opposing surfaces (50 and 52) is calculated independently of both the surface irregularities and any angular deviations of the three points of support (30, 32, and 34).