HEM Sapphire for Optical Applications 

HEM Sapphire Optical 100kg Boule

15" Diameter HEM Sapphire Boule
(130 kg)


GT’s 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 GT’s 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

Standard Window Transmission

Standard Transmission Chart

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.

  •  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

    HEM Sapphire Optical Components

    HEM Sapphire Optical Components

  • 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) 
  • Sapphire optics up to 15” in diameter, no thickness restrictions,

    Interferogram of 11” Diameter
    High-Performance Sapphire Window

  • Purity of 99.996% or better, (view: GDMS Purity Analysis of HEM Sapphire)
  • Low absorption sapphire
  • Transmitted wave front (TWE), of 1/10 wave peak to valley and better
  • Low damage, Super-Polished Optics available
  • Affordable “standard” polished optics available


HEM Sapphire Applications

There is an 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.  GT Crystal Systems is committed to supporting its customers as they develop new technical solutions using HEM Sapphire.


Please contact sapphiresales@gtat.com or call +1.978.745.0088 with any questions.