Sapphire (Sapphire, molecular formula Al₂O₃) single crystal is an excellent multi-functional material. It has high temperature resistance, good thermal conductivity, high hardness, infrared penetration and good chemical stability. At the same time, it is also a widely used single crystal substrate material, which is the substrate of choice for the current blue, purple, white light emitting diode (LED) and blue laser (LD) industry.
　　In the field of optical communication, sapphire crystal is not only used as a short-wavelength active device, but also as a polarizer of passive devices.
　　In the laser field, sapphire is an excellent laser dielectric material (such as Ti:Al₂O₃,Cr:Al₂O₃); In the field of superconductivity, sapphire crystal can not only produce Y series, La series and other high temperature superconducting films, but also grow new practical MgB₂ high temperature superconducting film (usually single crystal substrate in the production process of MgB₂ film will be chemically corroded);
　　It is widely used as an important window material for high energy detection and high power laser.