“Fused Silica” or “Fused Quartz” which is the amorphous phase of quartz (SiO2). When contrasted to borosilicate glass, fused silica has no additives; hence it exists in its pure form, SiO2. Fused silica has a higher transmission in the infrared and ultraviolet spectrum when compared to normal glass. Fused silica is produced by melting and re-solidifying ultrapure SiO2. Synthetic fused silica on the other hand is made from silicon-rich chemical precursors such as SiCl4 which are gasified and then oxidized in a H2 + O2 atmosphere. The SiO2 dust formed in this case is fused to silica on a substrate. The fused silica blocks are cut into wafers after which the wafers are finally polished.
Ultraviolet Grade Fused Silica – JGS1
Ultraviolet Grade Fused Silica wafers encompass a high transparency in the ultraviolet spectral range. The transmission in the VIS and UV is approx. 90 % hence only reflection losses and drops between 220 and 150 nm down to 0 %. In the infrared range, the comparable high OH-concentration of normally 1000 ppm which causes absorption bands for wavelengths > 1.2 μm.
Optical Grade Fused Quartz – JGS2
The transmission range of significantly cheaper JGS2 wafers is shifted towards longer wavelengths when compared with JGS1 wafers. In this case, UV-absorption starts below approx. 270 nm wavelengths, while in the VIS and IR the transmission is approximately 90 % up to approximately 2 μm wavelength as a result of lower OH-concentration (typ. < 300 ppm).
Full Spectrum Fused Silica – JGS3
These are wafers which are comparatively more expensive than the others. These wafers encompass very low OH-content (typ. < 10 ppm) showing a high transparency of > 80 % over a broad spectral range of approximately 200 nm – 3 μm, and approximately 90 % in the wavelength range 250 – 2.5 μm.
|Thickness||µm||100 and up||100 and up||100 and up||300 and up||400 and up||500 and up||500 and up|
|Primary reference flat||mm||32.5||32.5||32.5||57.5||Semi-notch||Semi-notch||Semi-notch|
|LTV (5mmx5mm)||µm||< 0.5||< 0.5||< 0.5||< 0.5||< 0.5||< 0.5||< 0.5|
|TTV||µm||< 2||< 2||< 2||< 3||<3||<5||<5|
|Warp||µm||≤ 30||≤ 30||≤ 30||≤ 40||≤ 50||≤ 50||≤ 50|
|Edge Rounding||mm||SEMI Std.||SEMI Std.||SEMI Std.||SEMI Std.||SEMI Std.||SEMI Std.||SEMI Std.|