Raman-scattering measurements of acoustic superlocalization in silica aerogels

Results of depolarized Raman spectroscopy on fractal silica aerogels are presented at frequencies from 0.3 to 50 cm-1. Three distinct vibration regimes are observed. In the fracton range, a power-law dependence of the Raman susceptibility on the frequency is found. It allows a determination of the superlocalization exponent d. Alternatively, with use of the "resistance" expression for the exponent d a spectral dimension d in fair agreement with previous measurements results. © 1988 The American Physical Society.