Aluminum oxide is commonly referred to as alumina or by its chemical formula, Al2O3. Corundum or α-alumina is the most common natural polycrystalline form of alumina. Sapphire is the single crystal form of alumina. It is a very durable and robust material for optical components as well as a gemstone of various colors.
Typical of many ceramics, alumina has very low electrical conductivity and is an electrical insulator. Alumina has a relatively high thermal conductivity and thermal shock resistance and can be used as, e.g., a high temperature insulator or heat sink in some applications. Alumina can be used in high temperature environments (to about 1800 °C or 3270 °F ) and is chemically inert which enables its use in a wide range of corrosive environments.
CeraNova has developed a high hardness, high strength alumina called CeraLumina™ that is transparent in the mid-wave infrared portion of the electromagnetic spectrum. CeraLumina is used in several applications requiring infrared transparency and its superior mechanical properties provide a significant performance advantage. In optical applications, high strength CeraLumina allows for thinner windows than sapphire which reduces adsorption losses and thermal emission. The high hardness of CeraLumina lends itself well to applications where scratch resistance and surface finish durability are vital. A non-transparent form of CeraLumina is also available for applications where superior thermal and mechanical properties are needed but transparency is not required.
Spinel is a naturally occurring mineral. It is popular in the jewelry industry as well as many commercial applications. The cubic crystal structure of spinel results in a very transparent single crystal and is an excellent quality gemstone. In the polycrystalline form, spinel is still highly transparent from the near ultraviolet (UV) region of the spectrum, through the visible (VIS) and well into the mid-wave infrared region (MWIR).
CeraNova manufactures a transparent polycrystalline form of magnesium aluminate spinel (Mg2AlO4) for several optical applications. Unique to CeraNova’s spinel material is its high optical quality combined with high strength. CeraNova’s transparent polycrystalline spinel has strength two to three times higher than other commercial spinels. Combined with CeraNova’s near net shape forming manufacturing and free form fabrication capabilities, visible and MWIR optics that were previously not available can now be readily produced. Flat plates up to several millimeters thick and 400 mm in length/width or diameter are available, as are 3D shapes including spherical and aspherical optical components.
Yttrium oxide, or yttria, has the chemical formula Y2O3. Polycrystalline yttria has a cubic crystal structure and can be produced with very high transparency. Yttria is not as strong as some other ceramics, but in both single crystal and polycrystalline form it has one of the broadest transmission bands of any oxide ceramic. Good transmission levels are possible from the UV, through the visible, and well into the MWIR regions of the spectrum. A comparison of the transmission properties of CeraNova’s transparent ceramics can be found on our EO/IR Windows Products page.
Another growing application space for yttria is as a laser host material. The polycrystalline form of transparent yttria allows for higher doping levels and better distribution of dopant elements leading to improved lasing. A number of wavelength specific lasers have been created based on yttria as the host material.
CeraNova’s transparent yttria windows and domes have a very fine grain microstructure which produce an optical surface that is far superior to large grain polycrystalline yttria. As with other ceramic components made by CeraNova’s processes, both simple and complex near-net 2D and 3D shapes can be readily produced.
The design, production, and application of composite materials for optical transparency is challenging largely due to the potential degradation in optical properties that can occur when two dissimilar materials are combined. New classes of optical composites have been developed with tailored microstructures to produce properties not possible in the single component materials. Properties can be tailored through compositional gradients or by combining individual, immiscible materials on very fine scale.
CeraNova was a member of Raytheon’s Nano-Composite Optical Ceramic (NCOC) material team where one such unique composite was developed under a four-year DARPA (Defense Advanced Research Projects Agency) project. This new optical composite provides a revolutionary improvement in IR-transmitting windows, combining a distinctive balance of optical and mechanical performance.
CeraNova is developing new and proprietary composite materials for optical components. We work with different oxides to customize material performance based on application requirements, i.e., by optimizing the mechanical vs. thermal vs. optical performance trade space to provide the best solution possible.