Interferometric measuring system

Details Interferometric measuring system Interferometric measuring system

1977-08-01

1980-02-12

Clark, Conrad J.

Optics: measuring and testing

By dispersed light spectroscopy

Utilizing a spectrometer

356359, 356371, G01B 902

Patent

active

041881249

ABSTRACT:
In an interferometric measuring system, a collimated monochromatic and coherent beam of light (1, I.sub.1 -I.sub.n)impinges on a grating 1 disposed parallel to the test surface 2. It has been found that in the above arrangement, a diffraction order (preferably the first diffraction order S.sub.1 -S.sub.4) of the light reflected from the face of the grating opposite to the test surface is always parallel to three diffraction orders of the radiation which after being first diffracted upon its first passage through the grating and reflected from the test surface is again diffracted upon its second passage through the grating. These four radiations (S.sub.1 to S.sub.4) generate two interference fields, the combination of which generates a beat pattern.
According to the invention, the angle of incidence of the radiation impinging onto the face of the grating opposite to the test surface is chosen in such a way (preferably from 0.5.degree. to 5.degree.) that the areas in which the beat patterns generate an additional field of interference fringes, related to .lambda./4 distances, from the test surface are a maximum.
When properly selecting pairs of angles of incidence and of distances between test surface and grating the resolution of the resulting fringe pattern (interference fringes symmetrically interleaved by beat fringes) is improved by the factor of 2, i.e. the distance between two fringes is related to a .lambda./4 distance from the test surface, as opposed to the interferometric methods known heretofore where the maximum resolution is defined by fringe distances related to .lambda./2 distances from the test surface.

REFERENCES:
patent: 3858981 (1975-01-01), Jaerisch et al.

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