Abstract

A simple visual test for the evaluation of concave diffraction gratings is described. It is twice as sensitive as the Foucault knife edge test, from which it is derived, and has the advantage that the images are straight and free of astigmatism. It is particularly useful for gratings with high ruling frequency where the above image faults limit the utility of the Foucault test. The test can be interpreted quantitatively and can detect zonal grating space errors of as little as 0.1 Å.

© 1972 Optical Society of America

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References

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  1. G. R. Harrison, R. C. Lord, J. R. Loofbourow, Practical Spectroscopy (Prentice-Hall, Englewood Cliffs, N.J., 1948).

Harrison, G. R.

G. R. Harrison, R. C. Lord, J. R. Loofbourow, Practical Spectroscopy (Prentice-Hall, Englewood Cliffs, N.J., 1948).

Loofbourow, J. R.

G. R. Harrison, R. C. Lord, J. R. Loofbourow, Practical Spectroscopy (Prentice-Hall, Englewood Cliffs, N.J., 1948).

Lord, R. C.

G. R. Harrison, R. C. Lord, J. R. Loofbourow, Practical Spectroscopy (Prentice-Hall, Englewood Cliffs, N.J., 1948).

Other

G. R. Harrison, R. C. Lord, J. R. Loofbourow, Practical Spectroscopy (Prentice-Hall, Englewood Cliffs, N.J., 1948).

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Figures (3)

Fig. 1
Fig. 1

Optical arrangement of the grating test. Nearly monochromatic light from the slit is diffracted in a parallel beam toward the flat. After reflection from the flat, the beam strikes the grating again which forms an image near the optic axis. The mask and diaphragm exclude light from the central image. The observer views the grating from a position just behind the knife edge while the latter is moved through the image. Shadow patterns are interpreted as in the standard Foucault test.

Fig. 2
Fig. 2

Diffraction angle errors produced by a grating containing a zone of anomalous ruling frequency. Equations in the text ignore grating curvature.

Fig. 3
Fig. 3

Experimental arrangement for electronic sensing. A TV camera replaces the observers eye behind the slit. Use of quartz or sapphire optics and a uv sensitive photocathode would permit observations to be made in the uv (essential for 3600 groove/mm gratings). The optical path should be purged with dry nitrogen if 1849-Å radiation is to be used.

Equations (10)

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n λ = d ( sin θ + sin i ) = d sin θ ,
n λ = d ( sin θ + sin i ) = d ( sin θ + sin θ ) .
n λ = ( d + δ d ) sin ( θ δ θ ) ,
n λ = d sin θ d cos θ δ θ + δ d sin θ
δ d sin θ = d cos θ δ θ .
n λ = ( d + δ d ) [ sin θ + sin ( θ + δ θ ) ]
n λ = θ d + d sin θ + d cos θ δ θ + δ d sin θ .
θ = 2 ( δ d / d ) sin θ .
δ S = [ 2 R / ( 1 + cos θ ) ] ( δ d / d ) sin θ
δ d = 1.1 × 10 6 δ S .

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