Linear and nonlinear optical properties of hydrated and dehydrated silica micro-spheres under an electric bias
Department of Physics, National Tsing-Hua University, Hsin-Chu, Taiwan
Corresponding author: a email@example.com
Revised: 18 April 2006
Published online: 22 June 2006
The linear refractive indices and nonlinear second-order susceptibility of hydrated and dehydrated silica micro-spheres are studied using attenuated total reflectance (ATR) and the second harmonic generation (SHG) method in direct transmission, respectively. A dramatic change of the effective dielectric constant of silica suspension under an electric bias was observed, which is attributed to particle redistribution in the fluid. Dielectric constants of dehydrated silica spheres change slightly under an electric field due to Pockels effect, for which we measure a linear electro-optical coefficient of r33 ∼3.4±0.7 pm/V. The transmission second harmonic generation comes from the third-order susceptibility χ(3), which is a coupling of two photons and the electrostatic field induced by the surface –OH charges as characterized by the Gouy-Chapman model. The SH signal from the dehydrated silica vanishes because of the loss of –OH groups on the particle surfaces. Dehydration of silica beads is irreversible. The optical properties of dried silica spheres do not recover their original hydrated state when distilled water is added.
PACS: 42.65.Ky – Frequency conversion; harmonic generation, including higher-order harmonic generation / 73.20.Mf – Collective excitations (including excitons, polarons, plasmons and other charge-density excitations) (for collective excitations in quantum Hall effects, see 73.43.Lp) / 78.66.Vs – Fine-particle systems
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2006