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%.
© 1965 Optical Society of America
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