Refractive index of silica aerogel: Uniformity and dispersion law

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Vol. 595; no. 1; pp. 183 - 186
• Main Authors: Bellunato, T., Calvi, M., Matteuzzi, C., Musy, M., Perego, D.L., Storaci, B.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 21-09-2008
• Subjects: Cherenkov detectors; Silica aerogel; Silica aerogel; Cherenkov detectors
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/j.nima.2008.07.072

Two methods for the measurement of the uniformity of the refractive index
n
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 500
MeV electrons traversing the aerogel. The beam can scan the full aerogel surface providing information on point to point variations of
n
.
The measurement of the dispersion law
n
(
λ
)
is also reported. An Xe lamp coupled to a diffraction grating provides the monochromatic source. The index for each
λ
is measured by the prism method at a corner of an aerogel sample. A Sellmeier functional form for
n
(
λ
)
is assumed, and the parameters best fitting the experimental data are given.