Lithium Aluminosilicate Transparent Glass-ceramic Welding With Femtosecond Laser

It has been the key and difficult point in the field of hard and brittle materials microfabrication to achieve a high-quality and stable welding of glass,which has become one of hotspot in this research direction in recent years.Lithium aluminosilicate transparent glass-ceramic is widely used in aerospace,astronomical observation,consumer electronics and other fields due to its excellent physical and chemical properties.Its high-quality welding has important application value as well as potential market prospects.In view of the need for high-quality connection of Li2O-Al2O3-SiO2(LAS)transparent glass-ceramic with an extremely low coefficient of thermal expansion,this thesis conducted experimental research on the modification and welding of LAS transparent glass-ceramic using femtosecond laser with a wavelength of 1030 nm and a pulse width of 300 fs combined with a long focal length scanning oscilloscope system.The main research results were as follows:1.The optical band-gap of LAS transparent glass-ceramic was 3.37 eV measured by Tauc plot method.The nonlinear photoionization process of LAS transparent glass-ceramic local modification caused by femtosecond laser at a wavelength of 1030 nm was a threephoton absorption process.Based on the free electron rate equation,the plasma density on the surface of LAS transparent glass-ceramic irradiated by femtosecond laser with different peak power density was calculated.The results showed that the induced plasma density reached the critical plasma density when the peak power density was 3.61 × 1012 W/cm2,and the LAS transparent glass-ceramics would undergo ablation at the interface.2.An experimental system for femtosecond laser processing of LAS transparent glassceramic was built.The ablation thresholds of LAS transparent glass-ceramic surface in single-pulse and multi-pulse irradiation modes and the variation of the ablation thresholds with the pulse irradiation number were investigated.The surface modification morphology as well as the component,glass network structure and elemental changes of LAS transparent glass-ceramic after irradiation with femtosecond laser were also analyzed.The results showed that the ablation thresholds of LAS transparent glass-ceramic were 2.21 J/cm2 and 1.38 J/cm2 under the single-pulse and 100-shot pulse irradiation modes for the femtosecond laser at a wavelength of 1030 nm,a pulse width of 300 fs and a repetition frequency of 100 kHz,respectively.Under the influence of incubation effect,the ablation threshold of LAS transparent glass-ceramic decreased in a power function with the increase of pulse irradiation number.The ultra-high peak power of the femtosecond laser pulse and the high temperature and pressure inside the glass-ceramic could make the glass network structure more unstable,and cause material surface removal and element migration in the irradiated region of the LAS transparent glass-ceramic.There was no new crystal phase was generated after femtosecond laser irradiating LAS transparent glass-ceramic.The welding process mainly consisted of the melting of the SiO2 glass phase to establish a strong connection at the LAS transparent glass-ceramic interfaces.3.The experimental study on LAS transparent glass-ceramic welding with femtosecond laser under different laser processing parameters was carried out.The effects of pulse energy,repetition frequency,scanning speed,deviation between focus and interface,and spacing between scanning line on weld seam width at interface and shear strength after welding were studied.The results showed that laser parameters(pulse energy,repetition frequency)and processing parameters(scanning speed,deviation between focus and interface,spacing between scanning lines)had an important influence on the LAS transparent glass-ceramic welding process with femtosecond laser.The window of LAS transparent glass-ceramic welding was enlarged and the shear strength up to 36.85 MPa was obtained by controlling the laser processing parameters.LAS transparent glass-ceramics could still maintain good light transmittance and sealing performance after welding.In this thesis,LAS transparent glass-ceramic with near-zero thermal expansion coefficient welding using femtosecond laser is carried out for the first time,which provides a new idea for thermally tempered glass welding with ultra-short pulsed laser.It has important practical value for the packaging of electronic devices and optical components.