158 kg sapphire single crystals were grown by horizontal directional solidification method. Bubble-free panels with usable rectangular dimensions of 457 mm x 914 mm x 38 mm (18 x 36 x 1.5 inches) can be cut from the crystals. These are the largest-area sapphire panels ever produced by any technique. Bubble-free sections of the crystal 300 mm x 457 mm and up to 60 mm thick (12 x 18 x 2.36 inches) can also be produced. Growths were performed with graphite heating elements under a controlled atmosphere with automated power control. Results of transmission measurements performed on 5 mm thick samples are presented and the transmission is similar to sapphire grown by other techniques.
As sensor technology and applications have advanced over the years, the size of sensor windows has grown substantially to satisfy current and future demands. Rubicon Technology, with their strong history in scaling sapphire crystal growth and large scale production processes, has successfully produced large sapphire blanks using a highly modified horizontal directional solidification process. Several prototypes have been synthesized up to 1.75 inches thick, 14 inches wide and 20 inches long. Crystal properties and optical characteristics such as transmission and refractive index homogeneity will be presented on several polished bubble-free windows with excellent results. This research sets the standard for high quality monolithic sapphire sheets large enough for use as seamless integrated optical windows in both military and civilian applications.