Low-Frequency and Low-Temperature Raman Scattering in Silica Fibers

Abstract

The Raman scattering spectrum of silica was measured to low temperature and very small frequency shifts. Strain-free cooling of a long silica-core fiber allowed us to investigate Raman scattering of the two-level tunneling systems to 1.5 K. A considerable central line broadening from relaxation of two-level tunneling systems is evident, although the predicted strong scattering contribution from resonant two-level tunneling centers at very low temperature and small frequency shift was not observed.