Study of the synthesis of SiO_2-TiO_2-GeO_2 gel glass for hollow waveguide application in CO_2 laser delivery

摘要

The SiO_2-TiO_2-GeO_2 sol-gel glass system was firstly ascertained to be the material to use in the fabrication of a hollow waveguide for application in CO_2 laser delivery.SiO_2-TiO_2-GeO_2 sols of various compositions were prepared by using Si(OC_2H_5)_4,Ti(OC_4H_9)_4 and Cl_3GeCH_2CH_2COOH as the precursors.It was found by viscosity and TEM analysis that the stability of the sol was weakened greatly when the conrtent of germanium dioxide reached 35% because of self-polycondensation of hydrolyzed Cl_3GeCH_2CH_2COOH.The sol with a composition of 40SiO_2 centre dot 30TiO_2 centre dot 30GeO_2 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 TiO_2 and GeO_2 phases separated from SiO_2 and that the material remained glassy.Compared with the IR reflexctivity peaks of silica glass,the IR reflectivity peaks of the SiO_2-TiO_2-GeO_2 gel glass are greatly broadened due to the formation of various mixed bonds between Ti,Si and Ge through bridging O atoms.The use of this material in a hollow waveguide structure for the delivery CO_2 laser is discussed on the bvasis of the calculated complex refractive index and transmission loss.The results show that a SiO_2-TiO_2-GeO_2 sol with a composition of 40SiO_2 centre dot 30GeO_2 is a good candidate material for this application.