Fused Silica

Fused silica is a noncrystalline (glass) form of silicon dioxide (quartz, sand). Typical of glasses, it lacks long range order in its atomic structure. It's highly cross linked three dimensional structure gives rise to it's high use temperature and low thermal expansion coefficient.

High chemical purity and resistance

Exceptionally good thermal shock resistance

Can be lapped and polished to fine finishes

Low dielectric constant

Low dielectric loss

Good UV transparency

Fused silica can made by melting some solid form of silica and cooling the melt sufficiently fast to avoid crystallization. A quite high temperature around 1650 to 1700 °C is needed – far above the glass transition temperature of many common optical glasses. The required heat can be provided by an electrically heated furnace or by a flame (Verneuille process) obtained with some combustion gas mixed with pure oxygen.

Fused silica is sometimes called fused quartz or quartz glass. However, it should be kept in mind that it is an amorphous material, while quartz is crystalline.