Optics: measuring and testing – By polarized light examination – With birefringent element
Patent
1994-08-29
1996-02-20
Turner, Samuel A.
Optics: measuring and testing
By polarized light examination
With birefringent element
356345, 356353, G01B 902
Patent
active
054933986
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a device with compact structure for observing test-piece surfaces for the measurement of deformations by the speckle-shearing method, having a coherent illumination of the test-piece surface, an image sensor (camera) and a two-beam interferometer used for imaging of the test-piece surface on the image sensor, the interferometer having two mirrors and a beam splitter.
With the speckle-shearing method, which is among others described in "Handbook for Experimental Stress Analysis, Ed. Christof Rohrbach, Publisher VDI 1989, p. 386-389", the test-piece surface to be tested and illuminated by coherent light is observed by camera takings, which consist of two optically superimposed partial images, which are slightly off-set with respect to each other. This off-set is produced by a double aperture or a prism in the imaging optical system. Both embodiments are not adapted to use of the phase shift technique introduced for interferometric measurements in combination with the electronic image evaluation.
Furthermore, no possibility of adjusting the shearing angle is provided.
DE-C-26 11 402 describes a process and a device for exactly adjusting the shearing off-set in a shearing interferometer system. The body of the basic interferometer consists of a beam splitter cube with terminal mirrors in both interferometer arms, which are formed as deviating prisms. Plane wave fronts in the interferometer region are achieved by collimating the beam path. The shearing off-set is adjusted by relative shifting of the deviating prisms. An imaging lens system is provided for detecting the object surface and for imaging on an image sensor.
A device known from U.S. Pat. No. 4,660,978 provides real time analysis of the distortion of wave fronts of an optical beam in the laboratory which are caused by the tested optical systems or are influenced thereby. The arrangement does not need a reference beam; it is formed as a shearing interferometer. The interferometer arms are terminated by plane mirrors and a parallel beam path is tested. An image of the test-piece surfaces onto the image sensor is not possible without supplementary aids.
In applied Optics, Vol. 13, No. 2, 1974, p. 233-234, a Michelson interferometer is proposed, wherein a diver gence of the field by use of concave mirrors is proposed for improving the resolution and increasing the applied energy. Two spherical concave mirrors having the same radius of curvature are adjusted in such a manner that the centers of their radii of curvature come to lie on the surfaces of the splitting cube. The images of the sources also fall onto these surfaces and generate interference orders, and thus reasons of symmetry in the interferometer structure.
U.S. Pat. No. 4,193,693 describes the adjusting mechanism/control of an interference spectrometer, wherein both interferometer arms are terminated by concave mirrors and wherein one of the concave mirrors is adjustably arranged in the direction of the beam path for modifying the optical path. Therein the used concave mirrors ("cat eyes") have the purpose of focussing the parallel beam path in a respective interferometer arm on to a small area detector arranged in the focus.
In Applied Optics, Vol. 14, No. 3, 1975, p. 618-622 the speckle-shearing interferometry for surface-like strain measurement is described, wherein the principle of the double aperture speckle interferometer serves as a basis. One works with a 4-fold aperture, wherein simultaneous, so to speak superimposed takings for 4 shear directions result. This superimposition is resolved to the individual shearing directions with evaluation of the takings by a Fourier filter technique.
U.S. Pat. No. 4,725,144 describes a system for comparative measurement (testing of form fidelity) of the surface form of optical elements (e.g. concave mirrors). A Twyman-Green interferometer with coherent illumination is used. The terminating mirrors of the two interferometer arms are test object and comparison object. For reducing the number of the observed orders of interferen
REFERENCES:
patent: 4193693 (1980-03-01), Schindler
patent: 4643576 (1987-02-01), Kanoh et al.
patent: 4660978 (1987-04-01), Wu
patent: 4725144 (1988-02-01), Nelson et al.
patent: 5076695 (1991-12-01), Ichihara
Applied Optics, vol. 24, No. 14, Jul. 15, 1985, pp. 2172-2180, "Fringe Scanning Speckle-Pattern Interferometry".
Applied Optics, vol. 14, No. 3, Mar. 1975, pp. 618, 620, 622, "Speckle-Shearing Interferometric Technique".
Applied Optics, vol. 13, No. 2, Feb. 1974, pp. 233-234, "Field Widened Michelson Spectrometer With No Moving Parts".
Merlino Amanda
Turner Samuel A.
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