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Journal of the Optical Society of America

Journal of the Optical Society of America

  • Vol. 55, Iss. 4 — Apr. 1, 1965
  • pp: 432–435

Total Hemispherical Emissivity of Sapphire

A. M. WITTENBERG  »View Author Affiliations

JOSA, Vol. 55, Issue 4, pp. 432-435 (1965)

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A calorimetric method is described which has been used to measure the total hemispherical emissivity of crystal-oriented sapphire. The results of two series of measurements are presented, one with the crystal C axis parallel to the surface normal (0° orientation) and the other with the C axis perpendicular to the normal (90° orientation). In the temperature range of -65° to 100°C the emissivities vary from 0.496 to 0.567 for the 0°-oriented sapphire and from 0.471 to 0.552 for the 90°-oriented material. Error analysis indicates that these results should be accurate to better than ±3%.

A. M. WITTENBERG, "Total Hemispherical Emissivity of Sapphire," J. Opt. Soc. Am. 55, 432-435 (1965)

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  1. D. W. McCarthy, Appl. Opt. 2, 591 (1963).
  2. A. M. Wittenberg, "The Measurement of the Total Hemi-spherical Emissivity of Materials Used in Telstar," presented at the Sixth National Symposium of the Society of Aerospace Material and Process Engineers, November 1963.
  3. Sapphires obtained from Linde Company, New York, New York.
  4. Distributed by Eppley Laboratory, Inc., Newport, Rhode Island.
  5. E. R. G. Eckert and R. M. Drake, Jr., Heat and Mass Transfer (McGraw-Hill Book Company, Inc., New York, 1959), p. 406.
  6. O. A. Saunders, Proc. Phys. Soc. (London) 41, 569 (1929).
  7. IGY Annals, Vol. 5, Part 6, Radiation Instruments and Measurements (Pergamon Press, Inc., New York, 1958), p. 436.
  8. The reduction of Eq. (1) to Eq. (2) requires some further discussion concerning the "nongray" character of the sample and the absorptivity of the test sphere, which is not felt to be of sufficient relevance to spend time on here. The author intends to discuss this subject in more detail in a future paper.
  9. H. O. McMahon, J. Opt. Soc. Am. 40, 376 (1950).
  10. D. Mergerian, Proc. Infrared Inform. Symp. 4, 146 (1959).
  11. American Institute of Physics Handbook, edited by D. E. Gray (McGraw-Hill Book Company, Inc., New York, 1957), Sec. 6, p. 108.
  12. L. E. Howarth (private communication).
  13. R. D. Olt, "Synthetic Sapphire, an Infrared Optical Material," presented at the Infrared Information Symposium, March 1958.
  14. The value of the Stefan–Boltzmann constant used here, σ = 5.67 × 10-12 W-cm-2-deg-4, which has been calculated from the physical constants, is the one accepted by most researchers. However, numerous experimental determinations have given a value about 1% higher than this figure. This still puzzling fact has not been included in our error analysis (see Ref. 5, p. 365).

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