High‐temperature infrared and dielectric properties of large sapphire crystal for seeker dome application

In this paper, large-sized (∅230 mm × 210 mm, 27.5 kg) sapphire was successfully grown by SAPMAC (sapphire growth technique with micro-pulling and shoulder-expanding at cooled center) method; and hemisphere dome (140 mm diameter, 5 mm thickness) was fabricated from as-grown boule. Also, its high temperature infrared transmission (2∼7 µm, 20–800°C) and microwave dielectric properties (8–16.5 GHz, 30–1300°C) were investigated. The experimental results show that sapphire crystal exhibits high infrared transmittance (3 μm, 80–86%), essentially negligible dielectric loss (4.9×10-5–3.7×10-4), but fairly high dielectric constants (e=9.4–12.5) in the temperature range of 30–1300°C. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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