The shape and value of optical non-uniformity are of great significance to optical materials and directly determine whether optical materials can process into finished components in optical systems. TiO2– SiO2 glass is usually used to prepare high-precision lightweight space mirrors and large-scale ground-based telescopes due to its low expansion. The corresponding relationship between the surface shape change and the temperature change of the glass prepared by CVD process needs to be verified. The shape of the silica glass with different doping contents is manufactured to 50×8 mm, and the surface shape of samples is polished to about 0.5λ (λ=632.8 nm). A ZYGO laser plane interferometer with a 100 mm aperture is used to test the samples' optical non-uniformity values and optical stability under the rapid change of temperature. The results show that the doping of TiO2 can significantly improve the optical stability of silica glass. When the sample is rapidly cooled from 80 to 20 , the change rate of PV value is only 0.01~0.02λ (λ=632.8nm). The morphology and numerical value (Δn=10ppm) of optical inhomogeneity can be used as optical transmission materials. Silica glass doped with 7.5-10wt% TiO2 has good optical stability, and the transmittance of visible light and near-infrared light is greater than 90%. Its optical inhomogeneity is in the order of 10-5, and its morphology has no apparent mutation. Therefore, it can be used as a reflective material and as a transmissive material in optical systems.
The distortion caused by temperature change in optical materials seriously impacts the accuracy and stability of optical systems, and it is vital to develop a transmission and reflection optical material with ultra-high optical stability. Doping TiO2 in silica glass can greatly reduce the thermal expansion coefficient of silica glass, improve the thermal stability of silica glass, and improve its optical stability. We used SiCl4 and TiCl4 as precursors to prepare glass materials with different titanium contents by CVD process in this work. After the precursors are thoroughly mixed, they enter the high-temperature furnace with a hydrogen-oxygen flame for chemical reactions. The granular SiO2 and TiO2 mixture generated by the reaction is deposited on the bottom of the furnace under gravity and sintered layer by layer to form a transparent glass body. The spectral transmittance and structural characteristics of glasses with different titanium contents were characterized by Raman spectroscopy and ultraviolet-visible-near infrared spectrophotometer to analyze the spectral transmittance and microstructure characteristics of the materials. The test results show that silica glass doped with 7.5- 10wt% TiO2 has good optical stability, and the transmittance of visible light and near-infrared light is greater than 90%. The doping of TiO2 makes the silica glass network show a specific ‘deaggregation’ phenomenon, but the tetrahedral framework of the silica glass is maintained. In addition to the tetrahedral form of Ti ions in the silica glass network, there is also the six-coordinated octahedral form.
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