Abstract

A new refractometer is described, based on the principle of the penetration of light into the rarer medium at total reflection. A transparent hemisphere with a slightly curved diametral plane makes point contact with the smooth surface of the sample to be measured. When viewed through the hemispherical surface, Newton’s black spot is visible. At the critical angle, the light is totally reflected at the hemisphere boundary, and the black spot diappears. The critical angle at which the spot is no longer seen can be translated into refractive index and measured with very simple equipment. Operation is unaffected by the index of a contact liquid and indices can be measured which are as high as the optical constants of the material available for the hemisphere. Measurements are described with a rutile hemisphere which renders the instrument useful to the index of the ordinary ray, n = 2.61.

© 1949 Optical Society of America

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References

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  1. A. H. Pfund, J. Opt. Soc. Am. 25, 351 (1935).
    [Crossref]
  2. Linde Air Products, Tonawanda, New York

1935 (1)

J. Opt. Soc. Am. (1)

Other (1)

Linde Air Products, Tonawanda, New York

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Figures (9)

F. 1
F. 1

Glass lens and prism combination (N = 1.52) in contact with fluorite plate (N = 1.43); angle of incidence less than critical angle for glass and air.

F. 2
F. 2

Glass lens and prism combination (N = 1.52) in contact with fluorite plate (N = 1.43); angle of incidence less than critical angle for glass and fluorite, greater than critical angle for glass and air.

F. 3
F. 3

Glass lens and prism combination (N = 1.52) in contact with fluorite plate (N = 1.43); angle of incidence greater than critical angle for glass and fluorite.

F. 4
F. 4

Schematic diagram of high index refractometer. Legend: N—source, D—diffusing plate, H—hemisphere, R—polished sample, C—focus of hemisphere, E—viewing lens, P—polarizer, T—telescope, S—scale.

F. 5
F. 5

Glass hemisphere (N = 1.60) in contact with fluorite plate (N = 1.43); angle of incidence less than critical angle for glass and air.

F. 6
F. 6

Glass hemisphere (N = 1.60) in contact with fluorite plate (N = 1.43); angle of incidence less than critical angle for glass and fluorite, greater than angle for glass and air.

F. 7
F. 7

Glass hemisphere (N = 1.60) in contact with fluorite plate (N = 1.43); angle of incidence greater than critical angle for glass and fluorite.

F. 8
F. 8

Plot of refractive index, n, vs. critical angle, θ, using as hemisphere constant, the approximate value for the ordinary ray of rutile, N = 2.61.

F. 9
F. 9

Plot of refractive index, n, vs. error in refractive index, dn, for an angular setting error, = 10′.