Rare earth doped silica glass can be used as the central material of optical fiber, which can be applied to the fiber laser. It becomes a focus in the field of laser materials. Compared with different kinds of rare earth elements, ytterbium is regarded as a promising laser nuclear fusion material due to its simple level structure, strong energy conversion efficiency, long fluorescent lifetime, etc. Nowadays, the usual fabrication method of optical fiber preform is the chemical vapor deposition (CVD). However, the preform made by CVD has low doping concentration, few kinds of doping elements, low homogeneity and hard-to-make into optical fiber of large core diameter. To solve these problems, a noble method, which is called non-chemical vapor deposition (Non-CVD), is developed.
Sol-Gel method is a kind of Non-CVD, which can perfectly solve the inhomogeneity in material. The glass has harmonious component since the whole process is at a liquid level.Sol-Gel method is a liquid phase synthesis method. The raw materials, including TEOS, absolute ethyl alcohol, ammonium hydroxide and deionized water, are uniformly mixed and become gel from sol through the hydrolysis and condensation. AlCl3 and YbCl36H2O are also added as the dopants. After that, heat the gel and let the hydroxyl and organic release, then we will be able to obtain the SiO2-doped powder. Combining with the laser melting technology, the ytterbium doped silica glass is made.
It is known from the DSC-TG curve of xerogel that during the heating process, water and organic are expelled from the system. It needs a holding period at 500 ℃ to ensure that the water and organic are expelled adequately. Moreover, the FTIR spectrum shows that after high temperature treatment the OH- concentration in the xerogel decreases dramatically.
The physical and spectrum properties of ytterbium doped silica glass are also tested. The Yb-doped silica glass which shows the amorphous state has good optical properties. The absorption spectrum and fluorescence spectrum demonstrate the typical absorption peak and emission peak of Yb3+, respectively. The density and refractive index of the glass are 2.409 g/cm3 and 1.462, respectively. The fluorescence lifetime () of the silica glass is 0.88 ms, the corresponding emission cross-section (emi) is 0.54 pm2, and the gain coefficient (emi) is 0.48 pm2m.
In conclusion, the Yb-doped silica glass is successfully prepared by the Sol-Gel method combined with laser melting technology, which possesses good physical and optical properties. This work is meaningful for preparing high-performance Yb-doped fiber, and even for developing the high power laser.
