THE GROWTH OF DOME-SHAPED SAPPHIRE CRYSTALS BY THE GRADIENT SOLIDIFICATION METHOD (GSM)

We describe the growth of sapphire single crystals, in dome geometry, by the gradient solidification method (GSM). Double walled molybdenum crucibles are utilized to grow the near-net-shape geometry. This significantly shortens the fabrication process of the dome to final dimensions, thus reducing the costs. The process is used to grow domes with different shapes (hemispherical and others), sizes (up to 6 inches in diameter) and crystallographic orientations (including the optical axis). Control of the thermal fields and growth rates is very important for the prevention of grain boundaries and scattering centers, as well as for the prevention of geometric distortions arising from surface tension effects.