Method and apparatus for making a contact-free measurement of th

Details Method and apparatus for making a contact-free measurement of th Method and apparatus for making a contact-free measurement of th

1985-01-22

1987-03-24

McGraw, Vincent P.

Optics: measuring and testing

By particle light scattering

With photocell detection

356354, 356359, G01B 902

Patent

active

046521313

ABSTRACT:
The invention is directed to a method and apparatus for the contact-free measurement of the actual position and/or of the profile of coarse surfaces. Laser light generated by a laser has at least two different wavelengths and is directed to the surface to be measured. A beam splitter is placed between the surface to be measured and the laser to split the laser light into a reference beam and a measuring beam. The reference beam is reflected on a reference plane surface. A speckle pattern is formed in the interferogram plane of the reflected light. From the speckle pattern, a bright laser speckle is selected for all wavelengths by means of a measuring diaphragm having a diameter less than that of a laser speckle. Behind the measuring diaphragm, the two wavelenths are separated from each other and the phase difference between the signals of the different wavelengths is measured. The phase difference is transformed into a signal proportional to the distance between the measuring point and the reference surface and is displayed. The reference light beam can be shifted in frequency with respect to the measuring beam by means of a heterodyne device.

REFERENCES:
patent: 3225177 (1965-12-01), Stites et al.
patent: 3647302 (1972-03-01), Zipin et al.
patent: 4005936 (1977-02-01), Redman et al.
patent: 4086808 (1978-05-01), Camac et al.
Dandliker et al., "Measuring Microvibrations by Heterodyne Speckle Interferometry", Optics Letters, vol. 6, No. 4, Apr. 1981, pp. 165-167.
Jones et al., "Holographic and Speckle Interferometry" Cambridge University Press, 1983, pp. 51-61, 198-239.

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