Abstract

Silver-based high-reflectance coatings that can withstand the humid and polluted conditions common in the open air have been developed for astronomical telescope optics. The successful designs incorporate a silver reflective layer with a copper underlayer and a stack of dielectric overlayers. Prototypes have been deposited and tested in a controlled environmental chamber and in true operating conditions on Kitt Peak in Arizona. The improved durability, which is due to the copper underlayer, has been investigated with analytical techniques, including Rutherford backscattering.

© 1985 Optical Society of America

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References

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  1. G. Hass, L. Hadley, “Optical Constants of Metals,” in American Institute of Physics Handbook, D. E. Gray, Ed. (McGraw-Hill, New York, 1972), pp. 6-124–6-156.
  2. L. D. Barr, Kitt Peak National Observatory; personal communication.
  3. I. Lubezky, E. Ceren, Z. Klein, “Silver Mirrors Protected with Yttria for the 0.5–14 -μm Region,” Appl. Opt. 19, 1895 (1980).
    [CrossRef] [PubMed]
  4. V. M. Dubkov, V. N. Rozhdestvenskii, “Protecting Reflecting Layers of Copper and Silver Against Tarnishing,” Sov. J. Opt. Technol. 50, 35 (1983).
  5. S. D. Browning, M. R. Jacobson, H. A. Macleod, R. H. Potoff, D. Y. Song, F. van Milligen, “Development of High Reflectance Coatings for Ground-Based Astronomical Instruments,” Proc. Soc. Photo-Opt. Instrum. Eng. 332, 310 (1982).
  6. P. J. Martin, H. A. Macleod, R. P. Netterfield, C. G. Pacey, W. G. Sainty, “Ion-Beam-Assisted Deposition of Thin Films,” Appl. Opt. 22, 178 (1983).
    [CrossRef] [PubMed]
  7. D. V. Keller, “Adhesion Between Solid Metals,” Wear 6, 353 (1963).
    [CrossRef]
  8. J. L. Stanford, H. E. Bennett, “Enhancement of Surface Plasma Resonance Absorption in Mirrors by Overcoating with Dielectrics,” Appl. Opt. 8, 2556 (1969).
    [CrossRef] [PubMed]

1983

V. M. Dubkov, V. N. Rozhdestvenskii, “Protecting Reflecting Layers of Copper and Silver Against Tarnishing,” Sov. J. Opt. Technol. 50, 35 (1983).

P. J. Martin, H. A. Macleod, R. P. Netterfield, C. G. Pacey, W. G. Sainty, “Ion-Beam-Assisted Deposition of Thin Films,” Appl. Opt. 22, 178 (1983).
[CrossRef] [PubMed]

1982

S. D. Browning, M. R. Jacobson, H. A. Macleod, R. H. Potoff, D. Y. Song, F. van Milligen, “Development of High Reflectance Coatings for Ground-Based Astronomical Instruments,” Proc. Soc. Photo-Opt. Instrum. Eng. 332, 310 (1982).

1980

1969

1963

D. V. Keller, “Adhesion Between Solid Metals,” Wear 6, 353 (1963).
[CrossRef]

Barr, L. D.

L. D. Barr, Kitt Peak National Observatory; personal communication.

Bennett, H. E.

Browning, S. D.

S. D. Browning, M. R. Jacobson, H. A. Macleod, R. H. Potoff, D. Y. Song, F. van Milligen, “Development of High Reflectance Coatings for Ground-Based Astronomical Instruments,” Proc. Soc. Photo-Opt. Instrum. Eng. 332, 310 (1982).

Ceren, E.

Dubkov, V. M.

V. M. Dubkov, V. N. Rozhdestvenskii, “Protecting Reflecting Layers of Copper and Silver Against Tarnishing,” Sov. J. Opt. Technol. 50, 35 (1983).

Hadley, L.

G. Hass, L. Hadley, “Optical Constants of Metals,” in American Institute of Physics Handbook, D. E. Gray, Ed. (McGraw-Hill, New York, 1972), pp. 6-124–6-156.

Hass, G.

G. Hass, L. Hadley, “Optical Constants of Metals,” in American Institute of Physics Handbook, D. E. Gray, Ed. (McGraw-Hill, New York, 1972), pp. 6-124–6-156.

Jacobson, M. R.

S. D. Browning, M. R. Jacobson, H. A. Macleod, R. H. Potoff, D. Y. Song, F. van Milligen, “Development of High Reflectance Coatings for Ground-Based Astronomical Instruments,” Proc. Soc. Photo-Opt. Instrum. Eng. 332, 310 (1982).

Keller, D. V.

D. V. Keller, “Adhesion Between Solid Metals,” Wear 6, 353 (1963).
[CrossRef]

Klein, Z.

Lubezky, I.

Macleod, H. A.

P. J. Martin, H. A. Macleod, R. P. Netterfield, C. G. Pacey, W. G. Sainty, “Ion-Beam-Assisted Deposition of Thin Films,” Appl. Opt. 22, 178 (1983).
[CrossRef] [PubMed]

S. D. Browning, M. R. Jacobson, H. A. Macleod, R. H. Potoff, D. Y. Song, F. van Milligen, “Development of High Reflectance Coatings for Ground-Based Astronomical Instruments,” Proc. Soc. Photo-Opt. Instrum. Eng. 332, 310 (1982).

Martin, P. J.

Netterfield, R. P.

Pacey, C. G.

Potoff, R. H.

S. D. Browning, M. R. Jacobson, H. A. Macleod, R. H. Potoff, D. Y. Song, F. van Milligen, “Development of High Reflectance Coatings for Ground-Based Astronomical Instruments,” Proc. Soc. Photo-Opt. Instrum. Eng. 332, 310 (1982).

Rozhdestvenskii, V. N.

V. M. Dubkov, V. N. Rozhdestvenskii, “Protecting Reflecting Layers of Copper and Silver Against Tarnishing,” Sov. J. Opt. Technol. 50, 35 (1983).

Sainty, W. G.

Song, D. Y.

S. D. Browning, M. R. Jacobson, H. A. Macleod, R. H. Potoff, D. Y. Song, F. van Milligen, “Development of High Reflectance Coatings for Ground-Based Astronomical Instruments,” Proc. Soc. Photo-Opt. Instrum. Eng. 332, 310 (1982).

Stanford, J. L.

van Milligen, F.

S. D. Browning, M. R. Jacobson, H. A. Macleod, R. H. Potoff, D. Y. Song, F. van Milligen, “Development of High Reflectance Coatings for Ground-Based Astronomical Instruments,” Proc. Soc. Photo-Opt. Instrum. Eng. 332, 310 (1982).

Appl. Opt.

Proc. Soc. Photo-Opt. Instrum. Eng.

S. D. Browning, M. R. Jacobson, H. A. Macleod, R. H. Potoff, D. Y. Song, F. van Milligen, “Development of High Reflectance Coatings for Ground-Based Astronomical Instruments,” Proc. Soc. Photo-Opt. Instrum. Eng. 332, 310 (1982).

Sov. J. Opt. Technol.

V. M. Dubkov, V. N. Rozhdestvenskii, “Protecting Reflecting Layers of Copper and Silver Against Tarnishing,” Sov. J. Opt. Technol. 50, 35 (1983).

Wear

D. V. Keller, “Adhesion Between Solid Metals,” Wear 6, 353 (1963).
[CrossRef]

Other

G. Hass, L. Hadley, “Optical Constants of Metals,” in American Institute of Physics Handbook, D. E. Gray, Ed. (McGraw-Hill, New York, 1972), pp. 6-124–6-156.

L. D. Barr, Kitt Peak National Observatory; personal communication.

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Figures (15)

Fig. 1
Fig. 1

Calculated reflectances of aluminum and silver with and without sapphire overcoats one quarterwave thick at 600 nm.

Fig. 2
Fig. 2

Performance and design of the coating consisting of a silver overcoat on aluminum.

Fig. 3
Fig. 3

Performance and design of the reflectance-boosting coating over silver.

Fig. 4
Fig. 4

Photographs of the coating surfaces after varying degrees of exposure to 94% relative humidity at 40°C. The photographs are of samples 5 cm wide. The substrates were microscope slides and the rear surface of the coatings could be photographed through them. A faint image of the filament of the light source can be seen in some of the photographs, especially (g) and (h). (a) Front and (b) rear surfaces after 20-h exposure of a coating of design: air|Al2O3|Ag|glass, (c) Front and (d) rear surfaces after 2 days of exposure of a coating of design: air|Ta2-O5|SiO2|Ta2O5|Al2O3|Ag|glass. (e) Front and (f) rear surfaces after 2 days of exposure of a coating of design: air|Ta2O5|SiO2|Ta2O5-|Al2O3|Ag|glass. (g) Front and (h) rear surfaces after 7 days of exposure of a copper-based coating of design: air|Ta2O5|SiO2|Ta2O5|Al2O3|Ag|Cu|glass.

Fig. 5
Fig. 5

Measured and calculated performance of the boosted silver coating with copper underlayer.

Fig. 6
Fig. 6

Comparison of reflectance between aluminum (lower curve) and the silver boosting coating with copper underlayer (upper curve) in the infrared region (2.5–15 μm).

Fig. 7
Fig. 7

Measured reflectance of coating after 5-min exposure to the atmosphere above a solution of 2-mliters 22% (NH4)2S in 18-mliters water. The silver in each case was 100 nm thick and the copper 40 nm thick.

Fig. 8
Fig. 8

Measured reflectance of a 100-nm silver layer with an underlayer of 40-nm copper. The points are theoretical figures from Hass and Hadley.1

Fig. 9
Fig. 9

Reflectance with respect to time for four different film designs exposed to the ammonium sulfide solution described in the text and in Fig. 7.

Fig. 10
Fig. 10

Reflectance with respect to time for the four different films of Fig. 9 with an expanded time scale to show the constant reflectance region for film with the copper underlayer.

Fig. 11
Fig. 11

Transmission electron micrographs of shadowed replicas of (a) a 100-nm silver film on glass and (b) a 100-nm silver film over a 40-nm copper film.

Fig. 12
Fig. 12

Results of a corrosion test in which a 100-nm silver film with copper and aluminum overlayers on opposite edges was subjected to atmospheric exposure above a solution of 2-mliters 22% (NH4)2S in 18-mliters water. (a) Appearance of the strip of silver next to the edge of the aluminum and (b) that of the silver next to the copper. The strip of uncorroded material in (b) is ∼0.7 mm wide or seven times that in (a).

Fig. 13
Fig. 13

Rutherford backscattering data showing the number of backscattered helium nuclei as a function of ion energy, which is proportional to the mass of the scattering nuclei in the film material. The highest atomic mass is that of silver, which appears as the peak on the right. The small concentration of copper on the film surface appears next as a very small peak, followed by the larger peak for the copper underlayer itself. The energies of the latter are reduced by passage of the ions through the overlying silver layer. Lower mass elements in the substrate appear on the left-hand side of the curve.

Fig. 14
Fig. 14

Reflectances of the samples exposed for 1 yr on Kitt Peak. Solid and dashed lines show reflectances before and after the test. (a) Reflectances for coating of design: air|Al2O3|Ag|glass; (b) reflectances for coating of design: air|Ta2O5|SiO2|Ta2O5|A12O3|Ag|glass; (c) reflectances for coating of design: air|Ta2O5|SiO2|Ta2O5|Al2O3-|Ag|Cu|glass.

Fig. 15
Fig. 15

Photographs of films after exposure for 1 yr on Kitt Peak: (a) coating of design: air|Al2O3|Ag|glass; (b) coating of design: air|Ta2O5|SiO2|Ta2O5|Al2O3|Ag|glass; (c) coating of design: air|Ta2O5|SiO2|Ta2O5|Al2O3|Ag|Cu|glass.

Tables (1)

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Table I Calculated Normal Spectral Emissivities at 6 and 10 μm are Shown for Aluminum, Gold, and Silver

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