Correlation between specific heat and change of refractive index formed by laser spot heating of tellurite glass surfaces

Correlation between the specific heat and the refractive index change formed by laser spot heating on tellurite glass surfaces has been investigated. The ternary tellurite glasses of TeO2–Na2O–Al2O3, TeO2–Na2O–GeO2 and TeO2–Na2O–TiO2 doped with 2 mol% of CoO were irradiated by a green light beam spot (532 nm) from a second harmonic generator of a Q switch pulse YAG laser. The refractive index map of the glass surface was measured with a He–Ne laser beam using a scanning ellipsometric technique, showing the formation of the refractive index dot patterns lower than the matrix by 0.05–0.22. The specific heat of the glasses was measured by CO2 laser flashing method. The glasses containing Al2O3 possessed the lowest specific heat among the three glass systems, giving the largest refractive index change on the glass surfaces. A good linear correlation between the reciprocal of the specific heat and the refractive index change was found in cases where the refractive index change was less than 0.1, suggesting that the refractive index change derived from the change of the fictive temperature of the glasses.