Our HEM™ sapphire is the most widely used optical sapphire in the world. HEM sapphire exhibits the unique capability of having a broad transmission range from the vacuum ultra violet (VUV), to the infrared (IR) spectrum. HEM sapphire combines high optical transmission, low transmitted wavefront distortion and outstanding mechanical-strength properties at high and low temperatures. Data shows that the homogeneity for all grades of HEM sapphire is in the 0.1 ppm range. This superior crystalline structure combined with low inclusions levels supports excellent performance in a wide range of optical window applications for aerospace and high power lasers and resonators.
HEM sapphire is grown using our highly automated HEM sapphire growth process. Developed over 40 years of continued process and performance improvements, this proven crystal growth method is known for its ability to control the heat input and also extract heat from the system with no mechanical movement. This precision control allows for the production of HEM sapphire in large sizes with highly homogeneous lattice structure and low scatter levels, with optical performance that is unmatched by other sapphire growth processes.
HEM Sapphire Optical Attributes
HEM sapphire is the leading material for highly sophisticated optical applications that require reliability, strength and a wide range of light transmittance. Sapphire transmits light over a broad wavelength range spanning from 0.15 to 5 microns.
- <50 ppm absorption @1064nm
- Low dn/dt over a wide range of lengths, (window temperature gradient does not cause image blur or foresight error)
- High mechanical strength for high-pressure and shock-loading applications
- Refractory temperature tolerance to within a few hundred degrees to its 2040°C melting point
- Chemical resistivity stable in many acid environments at high temperatures
- Attractive choice for laser host applications and use at cryogenic temperatures because of high thermal conductivity
- Thermal shock resistance because high strength and high thermal conductivity allow it to survive extreme thermal shock conditions
- High resistance to solarization radiation effects
- Hardness – excellent rain erosion resistance and low frictional coefficient
- High dielectric constant (9.39 from 1.0 MHz to 8.5 GHz)
HEM Sapphire Applications
HEM sapphire is available in sizes up to 22″ diameter in order to address the increasing demand in technical industries for large sapphire windows. Airplanes and UAVs, (Unmanned Aerial Vehicles), have advanced reconnaissance systems and other large view ports that sapphire is perfectly suited for. These advanced systems have many different light sources and detectors working at different wave lengths. Sapphire windows are capable of hosting these various equipment sets, working at different wavelengths under its one protective and efficient optical material. HEM sapphire has no thickness restrictions so windows can be utilized in pressurized and unpressurized situations. Sapphire is also increasingly viewed as a window material upgrade from Zinc Sulfide (ZnS) and Magnesium Fluoride (MgF2) for airborne applications. It is well known that sapphire is commercially available unlike other optical materials such as Alon and Spinel which are more expensive with weaker performance compared to HEM sapphire. Our Advanced Materials Group is committed to supporting its customers as they develop new technical solutions using HEM Sapphire.