Quartz Sight Glass

Specially prepared fused silica is also the key starting material used to make optical fiber for telecommunications. Because of its strength and high melting point (compared to ordinary glass), fused silica is used as the envelope of halogen lamps, which must operate at a high envelope temperature to achieve their combination of high brightness and long life. The combination of strength, thermal stability, and UV transparency makes it an excellent substrate for projection masks for photolithography. Due to the thermal stability and composition it is used in the semiconductor fabrication furnaces. Fused quartz has nearly ideal properties for fabricating first surface mirrors such as those used in telescopes. The material behaves in a predictable way and allows the optical fabricator to put a very smooth polish onto the surface and produce the desired figure with fewer testing iterations. In some instances, fused quartz has been used to make the individual elements of special purpose lens, such as the Zeiss 105mm f/4.3 UV Sonnar lens for the Hasselblad camera. This lens is used for UV photography, as the quartz has a lower extinction rate than lens made with more common flint or crown formulas. Translucent fused silica tubes are commonly used to sheathe electric elements in room heaters, industrial furnaces and other similar applications.