Linear and nonlinear optical properties of hydrated and dehydrated
silica micro-spheres under an electric bias |
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Authors: | C P Pang J T Lue |
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Institution: | (1) Department of Physics, National Tsing-Hua University, Hsin-Chu, Taiwan |
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Abstract: | 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. |
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Keywords: | 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 |
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