Infrared and Raman study of two-level systems in fiber optic quality a-SiO2 and a-SiO2:GeO2

With Raman scattering and far-infrared absorption spectroscopies two-level systems (TLS) have been examined in a series of fiber optic quality (SiO2)(1-x)(GeO2)(x) glasses. Even with large isovalent GeO2 doping, no Raman-active TLS spectrum is observed. When examined with the more sensitive far-infrared absorption technique some samples show a very weak TLS signature, but there is no correlation with the strength of the doping. It is found those internal strains in some glass samples account for this far-infrared activity. (C) 2002 Elsevier Science B.V. All rights reserved.