A comparison of the basic trace elements in fused quartz from rock crystal and synthetic fused silica is a good starting point in describing a base line for typical trace impurities in quartz materials. Different manufacturers as well as different measurement techniques will give slightly different values for the various constituents. Buyers should be aware that there are differences and care should be taken when selecting one for use.

In addition to the trace elements shown in the Typical Trace Elements: Fused Quartz and Synthetic Fused Silica table in the Appendix, there are other characteristics that are important in many applications. One such characteristic is the -OH content in the material used for optical fiber (especially the core) and sometimes for capillary tubing use.

For optical fiber use, certain hydroxyl (-OH) absorption bands may limit the performance. Material with a high concentration of -OH (600 to 800ppm) offers excellent transmission in the UV wavelength range from 190nm to 1064nm. It is well suited for broadband and laser applications in the UV if the energy densities are not too high. The transmission in the 800nm region is excellent, even with high doses of Gamma radiation. Certain regions in the visible and near IR are limited due to absorption around 724nm, 880nm, 944nm and 1242nm. There are useful windows (minimums) around 670nm, 800nm and 1030nm.

For longer visible and near-IR wavelengths a low -OH material should be used. Typical -OH contents are frequently below 1ppm and give only one minor absorption peak around 1385nm in the near-IR range. This type of material is used in optical fiber from 500nm to 2300nm.

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