CO₂ 激光改性溶胶-凝胶 SiO₂ 薄膜光谱及紫外纳秒激光损伤特性研究

This paper studied the physicochemical properties and laser damage resistance of sol-gel thin films conditioned with CO₂ laser. The results show that the surface roughness of the thin film after laser conditioning decreased from 14.08 to 9.76 nm, with a decrease of more than 30%. The thickness of the film decreases with the increase of the laser power. After laser conditioning of 20 W, the thickness of the film decreases by about 17%~28%. The mechanical properties, such as elasticity modulus and hardness, were improved after laser conditioning. The elasticity modulus increased from 1.5 to 6 GPa, and the hardness increased from 40 to 110 MPa. Results of Fourier transform infrared spectroscopy show that after laser conditioning, the main peak shifted from 1 125 to 1 120 cm^-1, and the average bridge bond angle between silicon and oxygen atoms became small.The reason is that during the CO₂ laser conditioning, the local temperature increase which accelerates the dehydration and condensation of Si-OH bond, and reduce the porosity and absorption. UV nanosecond laser was applied to the laser damage test of the film, and the results show that the laser damage area of the film after 12 W laser conditioning is smaller than the film without laser conditioning, and the laser damage threshold is increased from 4.8 to 7 J·cm^-2, which increased by 46%; However, the laser damage threshold after 16 and 20 W laser conditioning did not changes significantly, that is due to the ablation deposition occurred on the film's surface after high-power laser conditioning, which will affect the UV nanosecond laser damage threshold and can not effectively improve the laser damage resistance. The results of this study show that CO₂ laser conditioning can effectively improve the mechanical properties, including elasticity modulus, hardness of sol-gel SiO₂ films and the laser damage resistance. CO₂ laser's power has a great impact on the properties of the films. CO₂ laser conditioning is an effective technical means to improve the UV nanosecond laser damage resistance of sol-gel SiO₂ films.