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Optics

Optics Materials Data Sheet


SUPERSiC® Material Properties

 

Poco Graphite's SUPERSiC® silicon carbide is the material of choice for performance benefits aluminum, glass and other types of can offer. SUPERSiC attributes and strength, excellent and stability in cryogenic superior characteristics make the SUPERSiC material an ideal selection for industrial, space-based, and airborne/ground electro-optical applications.

 

Reflective optics manufactured from POCO’s silicon carbide material are uniquely suited to offer high optical quality mirrors for demanding applications. Substrates made from SUPERSiC are the preform foundation onto which chemical vapor deposited silicon carbide, or optical-grade silicon coatings are applied. Application of either coating provides a ready-made substrate for subsequent polishing and reflectance coat finishing.

 

 Shapes

 

POCO’s unique Chemical Vapor Conversion (CVC) process provides innovators the ability to design complex shapes and contours that would be expensive and difficult to manufacture by other methods. Conventional lathe and mill machining equipment and tools are used to produce a graphite preform to near-net shape. POCO’s process allows the freedom to create complex shapes with no more difficulty than would be experienced using aluminum. The CVC process completes the transformation from graphite to 100% silicon carbide.


Flats, spheres, aspheres or off-axis aspheric contours are easily manufactured with the SUPERSiC silicon carbide process. Shape-making ability is further complemented through conversion bonding or Reaction-Bonded Silicon Carbide (RSBC) technologies. Structural and optical designs may incorporate closed-cell and back plate features for added stiffness and weight reduction, while maintaining the structural integrity of a monolith.

 

Coatings


Polishing

 

SUPERSiC silicon carbide contains about 18% residual porosity, providing a substrate core that is inherently lightweight. Applying an encapsulating or selectively placed coating completes the substrate’s preparation. POCO offers three coatings as a polishing surface: Chemical Vapor Deposition (CVD) SiC, non-crystalline silicon and crystalline silicon. These coatings may be conventionally polished or, in the case of silicon, single-point diamond turned. All three options offer distinct advantages in performance, cost and lead time.


Applications


Scan Mirrors


Precise dynamic response from an optic within a scanning system is paramount to its successful operation. POCO scan mirrors made from SUPERSiC grade materials are lightweight but exceptionally stiff to provide the characteristics desired under rapid motion conditions. Designs may utilize open or closed-back structures for improved rigidity and stability. Laser-based applications where energy dissipation is a concern also benefit from SUPERSiC’s excellent thermal properties.


Lithography

Precision dynamic response is not limited to optic alone. Lithography applications benefit from the mechanical performance of SUPERSiC as well. SUPERSiC silicon carbide provides considerable mechanical stiffness through a wide range of temperatures. Applying a CVD SiC coating on SUPERSiC components ensures protection against particulate contamination, effectively sealing the parts and  

making them lightweight, stiff and clean – all factors highly desired for lithography processing.


Telescope – Structures and Mirrors


Assembling a telescope with metering structures and optics made from the same material is the "Holy Grail” of material configurations. Using SUPERSiC materials for both structures and mirrors is a major advance towards optimal performance by eliminating errors induced from mismatched properties.

 

Space-based applications, in particular, benefit considerably from low coefficient of thermal expansion and high stiffness of SUPERSiC materials. The suite of options available – increased elastic modulus from SUPERSiC-Si grade, CVD SiC coatings, Si claddings, reflectance coatings and others – provide multiple selections for any design project.

 

SUPERSiC Materials


POCO's unique conversion process produces the highest quality silicon carbide products available on the market today. This process starts with graphite material specially designed and manufactured for use as the precursor in the conversion process.

 

Near-net shaped parts are machined in graphite, purified, and subjected to a proprietary conversion process which substitutes pure silicon atoms for carbon atoms. During conversion, POCO has the ability to fuse parts so that they enter the furnace as an assembly of individual pieces and exit as a monolithic unit, with properties indistinguishable from those of a part originally made from one piece. This is done without the use of adhesives or other bonding agents. This conversion bonding process enables the creation of extremely complex, lightweight structures for aerospace optics such as spaceflight worthy, closed-back, off-axis or aspherical mirrors for satellite systems. These material and process advantages have placed POCO at the forefront of silicon carbide component development.

 

SUPERSiC

 

SUPERSiC is the base SiC of POCO, converted graphite.

 

SUPERSiC-3C

 

SUPERSiC-3C is SUPERSiC that has been coated with a 75 μm CVD SiC coating, which encapsulates the substrate and seals the surface. This material is ideal for low-cost optics and structures.


SUPERSiC-Si

 

SUPERSiC-Si SUPERSiC that has been infiltrated with high-purity silicon. SUPERSiC-Si has improved mechanical properties over SUPERSiC. This material is ideal for CVD SiC coating or silicon cladding.


SUPERSiC-Si-3C


SUPERSiC-Si-3C is SUPERSiC that has been infiltrated with silicon and then coated with a 75 μm CVD SiC coating, sealing the porosity. This material is ideal for space-based optics and structures.

 

SUPERSiC-Si-8C

 

SUPERSiC-Si-8C is SUPERSiC that has been infiltrated with silicon and then coated with a 200 μm CVD SiC coating. This material is ideal for large optics and lithography components.


SUPERSiC-Si-4S


SUPERSiC-Si-4S is SUPERSiC that has been infiltrated with silicon and then selectively cladded with a 100 μm silicon cladding. This material is ideal for Single-Point Diamond Turning (SPDT), for reduced lead time and total cost.