Refractive Index of SiO2, Fused Silica, Silica, Silicon Dioxide, Thermal Oxide, ThermalOxide

“Fused quartz” and “fused silica” are medium refractive-index glasses containing predominately SiO2 in the amorphous (non-crystalline) form. The word quartz usually refers to the natural crystal or mineral as opposed to the phrase “fused quartz” which refers to the glass that is created out of a manufacturing process which involves heating quartz crystals to temperatures of around 2000 degrees Celsius (which has lower refractive index).

Fused quartz has better ultraviolet transmission than most other common glasses (such as borosilicate glasses that have somewhat higher refractive indices), making it an ideal candidate for applications in the sub-400nm spectral region. Additionally fused quartz/fused silica have a low thermal expansion coefficient and are resistant to scratches, water, and acids. Normal varieties of fused quartz contain water which gives it strong absorption bands in the infrared, though there are water-free varieties commercially available. Its refractive index varies from 1.55 to 1.40 (for its transparent range: 160nm to 3000nm). Because fused silica is optically stable and consistent, many use it as a reference or standard for spectroscopic measurements. The details of its refractive index temperature dependence are also well studied.

For a typical sample of SiO2 the refractive index and extinction coefficient at 632.8 nm are 1.457 and 0.000. Below are files of complete refractive index and extinction coefficients. If the file is not available for download, you can request our proprietary file by clicking "Request".

  • Tab-delimited data file for unrestricted use
Wavelength (nm)

Refractive Index Reference - I. H. Malitson, JOSA, Vol. 55, Issue 10, pp. 1205-1208 (1965)

I. H. Malitson (1965) "Interspecimen Comparison of the Refractive Index of Fused Silica" JOSA, Vol. 55, Issue 10, pp. 1205-1208 doi:10.1364/JOSA.55.001205
Wikipedia: SiO2

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