Silica is one of the most abundant compounds in nature and comprises nearly one third of the Earth’s crust. It occurs in its cleanest form as pure quartz sand. Manufacturers call glass made from the purest silica either fused silica or fused quartz.
The difference between fused quartz and fused silica is that the former crystallises on cooling while the latter does not.
To make the glass, the sand is melted electrically to a very high temperature.
As this resulting glass has an extremely high viscosity it will form, cool and anneal but not crystallize.
The final product can appear transparent, opaque or translucent, depending on its future application. The glass is highly resistant to any thermal shock. It is also inert chemically to all solvents with the exception of hydrofluoric acid, which dissolves silica.
The glass has an excellent ability to transmit wavelengths of the ultraviolet range of the spectrum without fluorescence.
The fused silica will devitrify at a temperature of 1,100 °C if contaminants such as phosphorus, vanadium or sodium are present.
Ultraviolet-grade lenses are designed for use in laser electro-optics. They are capable of transmitting light wavelengths between 195 and 2100 nano metres.
The lenses themselves are usually between 6.35 to 50 millimetres in diameter. They use specific substrates and anti-reflection coatings when operating at wavelengths below 400 nm.
The lenses may come in a standard spherical shape to make plano convex, double convex and plano concave lenses, as rods or aspherical.
An asphere is a complex, almost parabolic surface shape that can reduce or even eliminate the aberrations associated with transmission through a standard spherically shaped lens. Such lenses are used in many laser cutting and welding operations in the automotive industry as they can focus a laser beam precisely on one spot.
A correct and precise manufacturing technique is vital for all fused silica applications in UV optics. If the glass is not properly ground or polished, it will retain a high micro roughness and even some micro fractures. The surface of the glass may appear fine but once a coating is applied, the micro fractures may graze or even spread into the coating itself.
For more information on fused silica applications, feel free to contact us at Multi-Lab. We are a globally renowned supplier and fabricator of Quartz glass and high purity/technical ceramics and have a wealth of knowledge so we can help you with your individual requirements.