Abstract: Frequency-scanning interferometry is used for measuring test objects having multiple surface regions. The regions are distinguished and can be measured based on different measuring criteria. Interference data is gathered for the imageable portion of the test object from a plurality of interference patterns taken over substantially the same imageable portion at different measuring beam frequencies. The interference data is evaluated to determine topographical measures of associated points on the test object. The topographical measures are compared against a benchmark to distinguish between points on the test object that are within a first of the surface regions from points on a boundary separating the first surface region from one or more other surface regions of the imageable portion of the test object. The interference data of points within the first surface region are further evaluated to a higher accuracy.

Abstract: A frequency-shifting interferometer gathers intensity data from a set of interference patterns produced at different measuring beam frequencies. A periodic function is matched to the intensity data gathered from the set of interference patterns over a corresponding range of measuring beam frequencies. Localized correlations involving phase offsets between the interfering portions of the measuring beam are used to inform a determination of a rate of phase change with measuring beam frequency corresponding to the optical path length difference between the interfering beam portions.

Abstract: Two common-path interferometers share a measuring cavity for measuring opposite sides of opaque test parts. Interference patterns are formed between one side of the test parts and the reference surface of a first of the two interferometers, between the other side of the test parts and the reference surface of a second of the two interferometers, and between the first and second reference surfaces. The latter measurement between the reference surfaces of the two interferometers enables the measurements of the opposite sides of the test parts to be related to each other.

Abstract: A scanning interferometer employs dual interferometer modules at different wavelengths to expand a dynamic range of measurement, a compound probe for measuring multiple surfaces, and a confocal optical system for distinguishing between the surfaces measured by the compound probe. Within the compound probe, miniature optics divide a test beam into two sub-test beams that are focused normal to different test surfaces. Both sub-test beams contain the different wavelengths. A separate interferometer monitors movements of the compound probe for producing absolute measures of the test surfaces.

Abstract: Flatness and thickness variation information concerning transmissive plane-parallel test plates is obtained from a grazing incidence interferometer modified to distinguish between superimposed interference patterns containing both types of information. The grazing angle of the interferometer is varied, and unique modulation frequencies of local fringe intensities within the superimposed interference patterns are identified. The local fringe intensities attributable to the different interference patterns are distinguished by their respective modulation frequencies.

Abstract: A scanning interferometer employs dual interferometer modules at different wavelengths to expand a dynamic range of measurement, a compound probe for measuring multiple surfaces, and a confocal optical system for distinguishing between the surfaces measured by the compound probe. Within the compound probe, miniature optics divide a test beam into two sub-test beams that are focused normal to different test surfaces. Both sub-test beams contain the different wavelengths. A separate interferometer monitors movements of the compound probe for producing absolute measures of the test surfaces.

Abstract: Flatness and thickness variation information concerning transmissive plane-parallel test plates is obtained from a grazing incidence interferometer modified to distinguish between superimposed interference patterns containing both types of information. The grazing angle of the interferometer is varied, and unique modulation frequencies of local fringe intensities within the superimposed interference patterns are identified. The local fringe intensities attributable to the different interference patterns are distinguished by their respective modulation frequencies.

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: An interferometer (10) includes a prism extender (50) appended to a prism (32) for directing a beam of light (42) into a recess (44) of a test piece (34). A first portion (42a) of the beam (42) refracts from a reference surface (54) of the prism extender (50) to an angle (.alpha.) of grazing incidence on a bottom surface (46) of the recess (44), and a second portion (42b) of the beam (42) reflects from the reference surface (54). The two portions (42 aand 42b) of the beam (42) recombine at the reference surface (54) forming an interference pattern indicative of differences between the reference surface (54) and the bottom surface (46) of the recess (44).

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).