The optical constants of quartz, vitreous silica and neutron-irradiated vitreous silica (I)

Abstract

The infrared reflectivity of three forms of silica, α-quartz, vitreous silica and neutron-irradiated vitreous silica (≈ 2.7 × 10 20 neutrons cm −2) has beenmeasured from 400–2000 cm −1. These data have been analysed by a Kramers-Kronig transform to give the real and imaginary parts of the complex dielectric constant. Considerable care has been taken to identify and minimize errors arising in the measurements of the reflectivity spectra and in the subsequent analysis. Data are presented for the optical constants, oscillator frequencies, band strengths and halfwidths of each band. The spectra for vitreous silica and neutron-irradiated silica show two regions of absorption which are not present in the crystalline form — a strong band is observed near 950 cm −1 and a broad band from 600–800 cm −1. A difference spectrum obtained by subtracting the spectrum of the imaginary part of the dielectric contrast for vitreous silica from the corresponding data for neutron-irradiated silica reveals more detailed structure in the form of a weak but sharp band at 620 cm −1. Interpretation of these results is contained in a companion paper.