Abstract: A moiré interferometer has an illumination system and an imaging system that share a common focusing optic, which preferably takes the form of a concave mirror. Within the illumination system, the common focusing optic collimates light en route to a test surface. Within the imaging system, the common focusing optic telecentrically images a grating pattern appearing on the test surface onto a fringe pattern detector.

Abstract: Compound diffractive optics are used in an interferometer for simultaneously measuring multiple surfaces, making multiple measurements of individual surfaces, conveying test beams multiple times, and aligning pairs of the diffractive optics with each other. Typically, the compound optics have multiple diffraction zones that reshape test beams for reflecting from test surfaces or for combining with reference beams. The multiple diffraction zones can also exhibit different optical qualities such as transmission and reflection for conveying the test beams to and from the test surfaces.

Abstract: An object fixturing system applies to an interferometer having a pair of diffraction gratings arranged to produce and recombine test and reference beams. The fixturing system positions an object between the diffraction gratings so that a test beam is incident on a surface of the object at a grazing incidence angle. A positioning fixture engages the object and a reference surface of the interferometer in moving the object to a measurement position on a window platform that transmits the test and reference beams. The fixture is then removed for a simultaneous measurement of an entire surface of the object, which can be clamped in place if necessary by a clamping window that also transmits the test and reference beams.

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).