Optical constants of silica glass from extreme ultraviolet to far infrared at near room temperature

TLDR

Silica glass optical constants are broadly consistent across the spectrum, yet measured refractive and absorption indices vary with manufacturing, impurities, and experimental methods. This work reviews existing refractive and absorption data for silica glass from 30 nm to 1000 µm and introduces new comprehensive formulas for the 7–50 µm range. The authors critically analyze literature values and derive analytic approximations that span 7–50 µm, supplementing the previously limited 0.21–7 µm range. Silica glass is opaque below 200 nm and above 3.5–4.0 µm, exhibits distinct absorption bands due to electrons, OH groups, and Si–O–Si vibrations, and the proposed formulas agree with experimental data and extend usable spectral coverage.

Abstract

We thoroughly and critically review studies reporting the real (refractive index) and imaginary (absorption index) parts of the complex refractive index of silica glass over the spectral range from 30 nm to 1000 μm. The general features of the optical constants over the electromagnetic spectrum are relatively consistent throughout the literature. In particular, silica glass is effectively opaque for wavelengths shorter than 200 nm and larger than 3.5-4.0 μm. Strong absorption bands are observed (i) below 160 nm due to the interaction with electrons, absorption by impurities, and the presence of OH groups and point defects; (ii) at ~2.73-2.85, 3.5, and 4.3 μm also caused by OH groups; and (iii) at ~9-9.5, 12.5, and 21-23 μm due to SiOSi resonance modes of vibration. However, the actual values of the refractive and absorption indices can vary significantly due to the glass manufacturing process, crystallinity, wavelength, and temperature and to the presence of impurities, point defects, inclusions, and bubbles, as well as to the experimental uncertainties and approximations in the retrieval methods. Moreover, new formulas providing comprehensive approximations of the optical properties of silica glass are proposed between 7 and 50 μm. These formulas are consistent with experimental data and substantially extend the spectral range of 0.21-7 μm covered by existing formulas and can be used in various engineering applications.