Abstract

An interferometric method is described for determining the absorption coefficients of metals from the change in phase accompanying the reflection of light at normal incidence. The reflecting layers in an interference filter are made of the metal being studied. From the optical thickness of the dielectric between the reflecting layers and the wavelength of the light transmitted, the phase change can be calculated. A monocromatic light source is not required, and with photographic methods it is possible to extend the measurements beyond the visible region. Results are given for silver and aluminum in the wavelength range of 3600A to 8100A. For aluminum the index of refraction is also given for this range. It was found that the dispersion of evaporated films of MgF2 increased with thickness. An interferometric method is described for studying the rate of growth of corrosion layers on films which have been exposed to air. Silver films could be exposed without any apparent corrosion. The oxide layer on aluminum films reached a maximum thickness of about 45A.

© 1951 Optical Society of America

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References

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  1. Handbuch der Physik (Verlag. Julius Springer, Berlin, 1928), Vol. XX.
  2. L. G. Schulz, J. Opt. Soc. Am. 41, 261 (1951).
    [Crossref]
  3. L. G. Schulz and E. J. Scheibner, J. Opt. Soc. Am. 40, 761 (1950).
    [Crossref]
  4. L. N. Hadley and D. M. Dennison, J. Opt. Soc. Am. 38, 492 (1948).
  5. L. G. Schulz, J. Opt. Soc. Am. 40, 690 (1950).
    [Crossref]
  6. S. Tolansky, Multiple-Beam Interferometry (Clarendon Press, Oxford, England, 1948).
  7. G. Hass, Optik 1, 2 (1946).
  8. R. Minor, Ann. Physik 10, 581 (1903).
    [Crossref]
  9. John Strong, Procedures in Experimental Physics (Prentice-Hall, Inc., New York, 1938), p. 375.
  10. G. Hass, J. Opt. Soc. Am. 39, 532 (1949).
    [Crossref]
  11. L. G. Schulz, J. Chem. Phys. 17, 1153 (1949).
    [Crossref]
  12. R. S. Sennett and G. D. Scott, J. Opt. Soc. Am. 40, 203 (1950).
    [Crossref]

1951 (1)

1950 (3)

1949 (2)

G. Hass, J. Opt. Soc. Am. 39, 532 (1949).
[Crossref]

L. G. Schulz, J. Chem. Phys. 17, 1153 (1949).
[Crossref]

1948 (1)

L. N. Hadley and D. M. Dennison, J. Opt. Soc. Am. 38, 492 (1948).

1946 (1)

G. Hass, Optik 1, 2 (1946).

1903 (1)

R. Minor, Ann. Physik 10, 581 (1903).
[Crossref]

Dennison, D. M.

L. N. Hadley and D. M. Dennison, J. Opt. Soc. Am. 38, 492 (1948).

Hadley, L. N.

L. N. Hadley and D. M. Dennison, J. Opt. Soc. Am. 38, 492 (1948).

Hass, G.

Minor, R.

R. Minor, Ann. Physik 10, 581 (1903).
[Crossref]

Scheibner, E. J.

Schulz, L. G.

Scott, G. D.

Sennett, R. S.

Strong, John

John Strong, Procedures in Experimental Physics (Prentice-Hall, Inc., New York, 1938), p. 375.

Tolansky, S.

S. Tolansky, Multiple-Beam Interferometry (Clarendon Press, Oxford, England, 1948).

Ann. Physik (1)

R. Minor, Ann. Physik 10, 581 (1903).
[Crossref]

J. Chem. Phys. (1)

L. G. Schulz, J. Chem. Phys. 17, 1153 (1949).
[Crossref]

J. Opt. Soc. Am. (6)

Optik (1)

G. Hass, Optik 1, 2 (1946).

Other (3)

Handbuch der Physik (Verlag. Julius Springer, Berlin, 1928), Vol. XX.

S. Tolansky, Multiple-Beam Interferometry (Clarendon Press, Oxford, England, 1948).

John Strong, Procedures in Experimental Physics (Prentice-Hall, Inc., New York, 1938), p. 375.

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Figures (6)

Fig. 1
Fig. 1

Drawings which show schematically the sequence of deposits for various type filters. The thickness t of the dielectric was usually selected to keep the integer N of Eq. (2) equal to unity for all arrangements except C, where it varied from about 4 to 10. For measuring the dispersion of MgF2, filter F1 of D was used with N varying from 1 to 6 for a wavelength of 5000A.

Fig. 2
Fig. 2

Graph showing the values of k/λ for silver as a function of wavelength. The curve locates the values found with the interferometric method, whereas the special points (× and ●) are from previous publications. (See references 7 and 8.)

Fig. 3
Fig. 3

Drawing A shows the experimental arrangement for producing double filters of the kind given in Figs. 1D, 1E, and 1F. Drawing B shows the taper of the MgF2 (deposit II) along the length of the glass substrate. The arrangement for measuring wavelengths is given in C; SS indicates various positions of the entrance slit of the spectrometer.

Fig. 4
Fig. 4

Graphs for aluminum. In A the special points indicate the values for n calculated from R values (see references 10 and 11), while the curve locates the values of n used in Eq. (1) during the calculation of k. Graph B gives the values of k/λ. Special points (× or ●) locate published values. (See reference 7 and H. O’Bryan, J. Opt. Soc. Am. 26, 122 (1936)).

Fig. 5
Fig. 5

The experimental arrangement for measuring photographically the transmitted wavelengths of the air-type filters of Fig. 1C.

Fig. 6
Fig. 6

Variation in the dispersion of MgF2 films as a function of thickness. The vertical scale gives the difference in index of refraction for wavelengths at 4400A and at 6400A. The broken line is an extrapolation to zero thickness.

Equations (5)

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tan ψ = 2 k n 0 / ( k 2 + n 2 - n 0 2 ) .
( 2 n 0 t / λ ) + ψ / π = N .
( N λ / n 0 ) 1 - ( N λ / n 0 ) i = ( ψ λ / n 0 ) 1 - ( ψ λ / n 0 ) i .
R = [ ( n - n 0 ) 2 + k 2 ] / [ ( n + n 0 ) 2 + k 2 ] .
( 2 n 0 t / λ ) + ( ψ A g + ψ A 1 ) / 2 π = N .