Study of the synthesis of SiO2–TiO2–GeO2gel glass for hollow waveguide application in CO2laser delivery

The SiO2–TiO2–GeO2 sol–gel glass system was firstly ascertained to be the material to use in the fabrication of a hollow waveguide for application in CO2 laser delivery. SiO2–TiO2–GeO2 sols of various compositions were prepared by using Si(OC2H5)4, Ti(OC4H9)4 and Cl3GeCH2CH2COOH as the precursors. It was found by viscosity and TEM analysis that the stability of the sol was weakened greatly when the content of germanium dioxide reached 35% because of self-polycondensation of hydrolyzed Cl3GeCH2CH2COOH. The sol with a composition of 40SiO2·30TiO2·30GeO2 was chosen as the coating solution because of its relatively high content of Ti and Ge atoms and its long lifetime of 30 days. It was confirmed by XRD analysis that no crystal TiO2 and GeO2 phases separated from SiO2 and that the material remained glassy. Compared with the IR reflectivity peaks of silica glass, the IR reflectivity peaks of the SiO2–TiO2–GeO2 gel glass are greatly broadened due to the formation of various mixed bonds between Ti, Si and Ge through bridging O atoms. The wavelength of the CO2 laser is included in this peak and a refractive index below one is obtained. The use of this material in a hollow waveguide structure for the delivery CO2 laser is discussed on the basis of the calculated complex refractive index and transmission loss. The results show that a SiO2–TiO2–GeO2 sol with a composition of 40SiO2·30TiO2·30GeO2 is a good candidate material for this application.