Refractive index of silica aerogel: Uniformity and dispersion law

Abstract: Two methods for the measurement of the uniformity of the refractive index within a single block of silica aerogel are described. One is based on the deflection of a laser beam induced by transverse index gradients. The second exploits the Cherenkov effect, measuring the emission angle of photons radiated by 500MeV electrons traversing the aerogel. The beam can scan the full aerogel surface providing information on point to point variations of . The measurement of the dispersion law is also reported. An Xe lamp coupled to a diffraction grating provides the monochromatic source. The index for each is measured by the prism method at a corner of an aerogel sample. A Sellmeier functional form for is assumed, and the parameters best fitting the experimental data are given. [Copyright &y& Elsevier]