Abstract

Interferometric testing of the flatness or straightness of ground surfaces of metals, granite, ceramics, and glasses has always proved difficult because of the extremely low specular reflection from these optically rough surfaces. At oblique angles of incidence the specular reflection coefficient of nonoptical surfaces increases rapidly, typically from near 0.01 at 75° up to, say, 0.50 at 85° and near 1.00 at 90° angle of incidence. By taking advantage of this enhanced reflection at oblique incidence and the brightness and spatial coherence of visible gas lasers, it becomes practical to use interferometric inspection of nonoptical surfaces. A novel double-pass oblique-incidence interferometer is described which enables testing of large pieces having a specular reflection as low as 1%.

© 1983 Optical Society of America

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References

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  1. J. B. Saunders, F. L. Gross, J. Res. Natl. Bur. Stand. 62, 137 (1959).
    [CrossRef]
  2. P. H. Langenbeck, Appl. Opt. 8, 543 (1969).
    [CrossRef]
  3. K. G. Birch, J. Phys. E 6, 1045 (1973).
    [CrossRef]
  4. P. Hariharan, Opt. Eng. 14, 257 (1975).
    [CrossRef]

1975

P. Hariharan, Opt. Eng. 14, 257 (1975).
[CrossRef]

1973

K. G. Birch, J. Phys. E 6, 1045 (1973).
[CrossRef]

1969

P. H. Langenbeck, Appl. Opt. 8, 543 (1969).
[CrossRef]

1959

J. B. Saunders, F. L. Gross, J. Res. Natl. Bur. Stand. 62, 137 (1959).
[CrossRef]

Birch, K. G.

K. G. Birch, J. Phys. E 6, 1045 (1973).
[CrossRef]

Gross, F. L.

J. B. Saunders, F. L. Gross, J. Res. Natl. Bur. Stand. 62, 137 (1959).
[CrossRef]

Hariharan, P.

P. Hariharan, Opt. Eng. 14, 257 (1975).
[CrossRef]

Langenbeck, P. H.

P. H. Langenbeck, Appl. Opt. 8, 543 (1969).
[CrossRef]

Saunders, J. B.

J. B. Saunders, F. L. Gross, J. Res. Natl. Bur. Stand. 62, 137 (1959).
[CrossRef]

Appl. Opt.

P. H. Langenbeck, Appl. Opt. 8, 543 (1969).
[CrossRef]

J. Phys. E

K. G. Birch, J. Phys. E 6, 1045 (1973).
[CrossRef]

J. Res. Natl. Bur. Stand.

J. B. Saunders, F. L. Gross, J. Res. Natl. Bur. Stand. 62, 137 (1959).
[CrossRef]

Opt. Eng.

P. Hariharan, Opt. Eng. 14, 257 (1975).
[CrossRef]

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Figures (7)

Fig. 1
Fig. 1

Measured specular reflection of fused silica in E and E polarized light for a wavelength λ = 0.6328 μm. Talysurf traces give some indication of the surface roughness resulting from the use of 9-, 12-, and 15-μm abrasives.

Fig. 2
Fig. 2

Schematic diagram of the optical configuration of the double-pass oblique-incidence interferometer.

Fig. 3
Fig. 3

Double-pass Twyman-Green interferogram of beam splitter and retromirror combination after final assembly.

Fig. 4
Fig. 4

Interferogram from center to edge of a polished 410-mm diam Pyrex plate.

Fig. 5
Fig. 5

Interferogram of 150-mm diam cast-iron tool following grinding with surface grinder.

Fig. 6
Fig. 6

Interferogram of 300-mm diam cast-iron tool following its use with a 15-μm abrasive.

Fig. 7
Fig. 7

Fused silica lap of 254-mm diameter after grinding with a 25-μm abrasive.

Equations (1)

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R a = 1 L 0 L | Δ h | d L ,

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