Adsorption of water on porous Vycor glass studied by ellipsometry

The variation of the optical properties of porous Vycor glass (Corning, Mod el 7930) under different relative-humidity conditions was studied. The adso rption of water into the glass pores was investigated with spectroscopic el lipsometry. The change of the refractive index was Deltan similar to 0.04 b etween 5% and 90% relative humidity. A Linear relation between the ellipsom eter parameter tan Psi, the amount of water adsorbed in the glass pores, an d information about the pore-size distributions was established. The result s are in accord with the values obtained from N-2 isotherms, transmission e lectron microscope micrographs, and the manufacturer's specifications (radi us of similar to 20 Angstrom). The possibility of using this material as a transducer for implementation in a fiber-optic sensor to measure humidity w as evaluated. (C) 2001 Optical Society of America.