Fused silica / quartz optical component : a complete guide
Quartz / Fused silica is a very interesting material due to the combination of many interesting properties. It is fully transparent with very good transmission from UV to IR, have a high resistance to water and chemical elements, and having a very low Coefficient of Thermal Extension can resist even better than borosilicate to thermal shock.
Fused silica specifications
Below table shows the specifications for the common Fused Silica on the market
|Metal impurities||5 ppm||20-40 ppm||40-50 ppm||1 ppm||1 ppm|
|Birefringence constant||2-4 nm/cm||4-6 nm/cm||4-10 nm/cm||5 nm / cm||3.54 nm/cm|
|Manufacturing process||Synthetic CVD||O2-H flame melting||Electrical melting||Synthetic CVD||Synthetic CVD|
|Density||2.20 g/cm3||2.20 g/cm3||2.20 g/cm3||2.20 g/cm3||2.20 g/cm3|
|Abbe constant||67.6||67.6||67.6||2.20 g/cm3||67.8|
Differences between fused silica and quartz
Fused Silica, Quartz, Fused Quartz, Quartz Glass, Silica, Silica Glass, all these names are confusing and often not very well defined by their users. See below definitions about these terms so you will understand them better:
- Quartz : is usually used to describe natural crystalline quartz, by extension is used as a generic term for pure SiO2 (Silicon Dioxyde) crystals & glass.
- Silica : is pure non-crystalline SiO2 (Silicon Dioxyde), sand is made of silica but is not pure Silica.
- Fused Silica : transparent non-crystalline material made of pure Silica by deposition at high temperature. By extension is also used to cover Fused Quartz material.
- Fused Quartz : Pure Si02 material made by melting of crystalline quartz grains by electrical furnace or flame fusion.
- Quartz Glass & Silica Glass refers to respectively Fused Quartz and Fused Silica
Please note that normal glass is also mainly made of SiO2 but is not pure SiO2, other chemical elements are also added like NaO2 and other elements.
Optical elements made from fused silica / quartz
Fused silica / optical quartz are very commonly used for most of optical components :
- Mirror substrate
- Transparent quartz tubes
- Machined quartz components
- Optical wafers
Key advantages are that the raw material is rather affordable and easy to source, relatively easy to be machined, and highly resistant to chemicals and temperatures (can be used up to 1000°C).
Current trends :
- Fused silica wafers are currently in high demand for microwave and millimeter-wave circuits.
- UV optical components are increasingly used in sterilization systems, due to the fused silica good UV transmission a good share of these optical components are made in it.
Limitations : Fused silica cannot be diamond turned, so it may not be very recommandable material for aspherical lens.
Where to buy fused silica / quartz optical component ?
Most of precision optics suppliers are providing optics made of fused silica. The material is rather easy to work with and therefore contrary to Sapphire doesn’t need specific equipment to be cut and polished.
Key questions in the selection of your fused silica optics supplier is the complexity of the parts and optical specifications tightness, ability to provide an optical coating on the optics can be critical too.
Don’t hesitate to contact SINOPTIX to get information or a competitive quote on your quartz optics: