Fused silica is a widely utilized material in the optics industry for manufacturing essential components like lenses, windows, mirrors, prisms, and beamsplitters. Known for its precision and consistent optical performance, fused silica is often the preferred material for high-quality optics.

Its low thermal expansion coefficient provides significant thermal stability, which makes it resistant to thermal shocks, an important quality for applications requiring high durability under varying temperatures.

Additionally, fused silica exhibits high chemical resistance and minimal fluorescence, making it suitable for demanding environments. There are various types of fused silica, with UV-grade and IR-grade fused silica being the most commonly used due to their unique spectral transmission properties.

UV-Grade Fused Silica

UV-grade fused silica is manufactured through a synthetic process called flame hydrolysis, where high-purity silicon is oxidized to produce a material with high transmittance in the ultraviolet (UV) spectrum.

This high transmission makes it suitable for applications involving UV light, but there are specific absorption dips around 1.4 µm, 2.2 µm, and 2.7 µm due to hydroxide (OH⁻) ion impurities. These dips limit its effectiveness for some near-infrared (NIR) applications, as the presence of OH⁻ ions absorbs light energy at those wavelengths.

IR-Grade Fused Silica

IR-grade fused silica, on the other hand, is designed with fewer OH⁻ ions, making it more suitable for near-infrared applications. By reducing the concentration of hydroxide ions, either through melting high-quality quartz or employing specialized manufacturing methods, IR-grade fused silica achieves higher transmission in the NIR spectrum while offering reduced transmission in the UV range.

This makes IR-grade fused silica an ideal choice for applications requiring minimal absorption in the NIR, such as those involving infrared optics.

With the development of lasers operating around the 2 µm wavelength—such as thulium (2080 nm) and holmium (2100 nm) lasers—there has been a surge in applications focused on the 2 µm region. Given that this wavelength is close to one of the OH⁻ absorption peaks in UV-grade fused silica, IR-grade fused silica becomes a more suitable choice for such applications.

Using UV-grade silica near these absorption peaks could lead to excessive heat buildup and potential damage, whereas IR-grade fused silica mitigates this risk. However, IR-grade fused silica often comes with higher costs and reduced availability compared to UV-grade options.

Choosing the correct type of fused silica for an application requires a clear understanding of the operating wavelength range. Notch Optics provides optical components made from both IR-grade fused silica (Corning 7979) and UV-grade fused silica (Corning 7980), catering to a wide range of wavelength-specific needs.