Thermo-optic coefficient in some hybrid organic/inorganic fast sol–gel glasses

We have investigated the effect of organic content in hybrid organic/inorganic glasses prepared by the sol–gel process on the thermo-optic coefficient dn/dT. The organic phase consisted of homogeneously dispersed methyl groups within an inorganic silica matrix. Analysis of Fresnel reflectance temperature dependence of an optically polished sample-surface yielded the desired value, with an accuracy of 10−5/°C. A negative linear dependence of the thermo-optic coefficient on the volumetric thermal expansion coefficient β was obtained, dn/dT[10−4/°C] = −1.1–0.45β[10−4/°C]. Using Prod’homme’s model, a negative value was derived for the electronic polarizability coefficient Φ = (−1.8 ± 0.3) × 10−4/°C. The negative sign of Φ is attributed to isolation of the silica matrix sections by the methyl groups, causing the sections to distance upon increase in temperature.