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

In this paper, large-sized (0230 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 (ε=9.4-12.5) in the temperature range of 30-1300°C.