HEM® Sapphire for Optical Applications

HEM® Sapphire Windows are the most widely used synthetic sapphire in optical applications. Our superior optical quality sapphire is available in large sapphire window sizes of 23” diameter with unrestricted thickness. HEM Sapphire C-plane Sapphire Windows are available up to 12” in diameter.

HEM Optical Sapphire material exhibits the unique capability of having a broad transmission range, (150 nm to 5500 nm), where other synthetic sapphire have absorption bands. HEM Sapphire transmission and homogeneity are the highest in the industry and it is the most widely used for sapphire reconnaissance windows, sapphire domes and sapphire lenses.

Your sapphire window performance is only as good as the bulk sapphire material it is made from. HEM Sapphire properties are proven to combine 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, with the highest grades better than 0.05 ppm. HEM Sapphire Windows are currently performing in uncompromising environments in Aerospace, High Power Lasers (HEL) and Astronomy applications.

HEM Sapphire is produced in our proprietary HEM growth systems and processes. Do not be fooled by other producers who claim to have the same HEM technology, they do not. We have over 45 years of process development and R&D experience available to help our customers. Our sapphire processing “know-how” is applied to our customer’s unique requirements so that maximum performance is achieved in the final sapphire product.

HEM Sapphire is the #1 leading sapphire material for highly sophisticated optical applications that require reliability, strength and a wide range of light transmittance. HEM Sapphire transmits light over a broad wavelength range spanning from 0.15 to 5.5 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)


Applications

Large HEM Sapphire Windows are currently operating on the most advanced aerospace platforms. These 23” diameter sapphire aerospace windows are flight and performance proven with wave front values of 1/10 wave, high optical transmittance, strength and durability. Large sized HEM Sapphire Windows are replacing ALON windows because of superior performance, lower cost and immediate availability. Flight safety testing has proven that HEM Sapphire Windows are fit for pressurized applications where the HEM Sapphire Window is the only barrier between the flight crew and the outside environment.

Large C-plane HEM Sapphire windows are distinguished for being the largest and highest quality non-birefringent sapphire optics available in the marketplace. This non-birefringent material excels for use in laser windows, High Energy laser (HEL) and laser mirrors because of hardness (9 on the mohs scale), thermal shock resistance and high laser damage threshold (LDT). 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 HEM Sapphire is commercially available unlike other “promising” specialty optical materials such as Alon and Spinel whom are more expensive and unable to deliver on their promised performance.

Our Advanced Materials Group is committed to supporting its customers with new sapphire solutions to address their unique needs.

HEM Sapphire for Mechanical Applications

HEM Sapphire is used in many mechanical applications because of its large size, strength, abrasion resistance and chemical stability. HEM Sapphire has undergone extensive compressive and tensile strength testing at many different temperatures in order to understand its intrinsic failure modes and suitability for different applications. HEM Sapphire material is used in high operating temperatures above 1,200 degrees Celsius because of its thermal shock resistance. However, it is critical to leverage sapphire’s intrinsic strength by using the proper optical fabrication equipment and processing know-how. Low damage operations yield high-strength sapphire parts. Moreover, sapphire’s anisotropic nature requires that crystallographic orientations be optimized for the direction of forces and temperatures to which the component will be subjected. We have done the mechanical testing and analysis and will guide our customers with this knowledge.

Sapphire glass replacement is increasingly taking place as sapphire easily outperforms glass in mechanical applications. Even the most engineered glasses cannot compete with HEM Sapphire. Leverage over 45 years of Sapphire growth, fabrication and testing knowledge to enhance performance in your mechanical applications.

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Attributes

  • Melting point of 2040 C
  • Hardness of 9 on the mohs scale
  • High conductivity at cryogenic temperatures
  • Inert to chemicals at high temperatures
  • Low coefficient of thermal expansion
  • High compressive strength
  • High flexural strength at elevated temperatures
Expansions

Applications

Mechanical HEM Sapphire applications include; sapphire wafer carriers, sapphire dental brackets, sapphire fire windows, sapphire view ports, sapphire nozzles, sapphire bearings, sapphire blades, sapphire tubes, sapphire jewel bearings and sapphire transparent armor to name just a few. HEM Sapphire will safely operate where other structural materials will fail. The current and emerging engineering applications for mechanical Sapphire rely on consistent mechanical strength, purity and orientation homogeneity. GTAT’s unique HEM growth processes and extensive fabrication capabilities are fueling the replacement of less optimized crystal and glass materials with HEM Sapphire.

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Features and Highlights

Sapphire optics up to 22” in diameter, no thickness restrictions

Purity of 99.996% or better, (view: GDMS Purity Analysis of HEM Sapphire)

Low Absorption Optical Sapphire, absorption <50 ppm at 1064

Transmitted wave front (TWE), of 1/10 wave peak to valley and better

Low damage, Super-Polished Optics available

Affordable “standard” polished optics available

No thickness restrictions

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