SPIE Defense, Security and Sensing 2013 was held last week in Baltimore, MD. There was a very interesting paper on large sapphire optical windows. Rubicon Technology’s Dr. Jonathan Levine, Director of Technical Business Development, talked about recent advances in making very large sapphire optical windows from his paper, “Synthesis and Characterization of Large Optical-Grade Sapphire Windows Produced from a Horizontal Growth Process,” that he presented at the conference.
As sensor technology and applications, in defense and aerospace in particular, have evolved, the size requirements for sapphire sensor windows have grown substantially. Dr. Levine detailed how Rubicon successfully produced very large sapphire blanks using a highly modified horizontal directional solidification process. This new method, named the Large‐Area Netshape Crystal Extraction (LANCE) system is currently able to produce crystals of several different orientations weighing up to 50 kg with plans to expand the process to larger 100 kg sapphire crystals.
Based on a different technique than Rubicon’s ES-2 method, Levine’s team used the LANCE method because it produces plates or slabs of sapphire instead of cylindrical boules. Using LANCE is advantageous since the near-net shape dramatically reduces machining and associated fabrication costs. Further, since the melt is horizontal, capillary forces play a minimal role during growth and the crystal is not limited in size or thickness as compared to edge‐defined film-fed growth (EFG) crystals.
According to Levine, Rubicon has been able to synthesize several prototypes up to 1.75 inches thick, 14 inches wide and 20 inches long. The 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.
Sapphire is very good for defense and aerospace applications due to its excellent transmission in the UV through IR spectrum, high impact durability, and corrosion resistance in harsh environments. Sapphire applications include missile domes, transparent armor systems, FLIR and enhanced vision systems for aircraft, and shaped optics for land, air and sea vehicles.
For Further Reading
Rubicon Technology, Rubicon Technology Develops New Sapphire Crystal Growth Platform to Manufacture Large Optical-Grade Windows for Military and Industrial Applications, http://phx.corporate-ir.net/phoenix.zhtml?c=215281&p=irol-newsArticle&ID=1724966&highlight=
SPIE Defense, Sensing and Security 2013, http://spie.org/x6765.xml?WT.svl=mddce7