Current status of sapphire for optics

Sapphire has been used for many optical applications. However, smaller sizes have been used, even though the Heat Exchanger Method (HEM) has produced 20 cm diameter crystals. New generation systems require outstanding optical properties, high strength, and abrasion and thermal shock resistance. Therefore, the choice is limited to sapphire. Crystals up to 34 cm diameter, 65 kg have been grown by HEM, and it is planned to scale up the size to 50 cm diameter. In addition to larger size, the optical quality has been improved to cover the vacuum ultraviolet and the near infrared wavelengths. Fabrication technology was advanced to fabricate larger size, higher precision optics cost effectively. Improved transmitted wavefronts and higher quality surfaces have been produced to address current applications.