The refractive index of aerogel has been measured to obey, in rough agreement with the formula of Clausius-Mosotti, the relation where is the density of the material. Typically, aerogel can be produced in blocks of 100 mm sides. The optical quality of aerogel is determined by the homogeneity of the gel.
Absorption hence dominates at nm.
At nm, the diffusion length is of the order of 10 mm. Due to Rayleigh scattering, the directionality of the radiated Cherenkov light is somewhat lost, and classical mirror focusing techniques for light collection become difficult or inadequate.