| Sol-gel SiO2 and ZrO2 optical films, with its unique properties such as low absorption and low dispersionin in the visible and near-infrared spectral regions, the high chemical and thermal stabilities, and the good laser-induced damage resistance, as well as the simple deposited process and low cost, have proved to be a potential candidate for the optical films in high-power lasers. So it has extraordinarily concerned by many ICF research laboratories. Unfortunately, sol-gel SiO2/ZrO2 multi-layer HR films have very serious infiltration, which has restricted its layers coating and the laser-induced damage threshold (LIDT) greatly. Furthermore, the lack of a good knowledge of the laser damage mechanism of sol-gel optical films have greatly bottlenecked its wide application, and thus restricted the development of the sol-gel optical films.In this dissertation, optical characteristic and high laser damage behaviors of the single-layer SiO2, single-layer ZrO2, two-layer and multi-layer ZrO2/SiO2 have being carefully researched. Ellipometry, FT-IR, AFM and XPS are used to investigate the effects of infiltration by post trestments and pre-fill methods of the two layer SiO2/ZrO2 thin films. Damage threshold of the monolayer, two-layer and multi-layer films are measured by Nd:YAG Laser (1064nm). According to the damage morphology as well as the thermal dynamic response and microscopic observation, we set an explanation to why the chemical films have larger LIDT than the physicals. The main contributions are summarized as follows:1). The high quality colloidal suspension of ZrO2 and SiO2 can be prepared in the proper experiment conditions and in the proper chemical composition matches. The experiment chemicals are Zr(OPr)4, ammonia liquor, ethanol, PVP and so on.2). The infiltration exists between the multi-layer ZrO2/SiO2 film based on Ellipometry and XPS investigation. The results showed that infiltration was serious and almost happened complete infiltrating when ZrO2 deposited on SiO2. On the contrary, the infiltration was better when SiO2 deposited on ZrO2.3). The ammonia and heat post-treatment to SiO2 result in the thickness decreasing, the refractive index increasing and the porous ratio decreasing. Judging from microcosm, the SiO2 grains approach each other because of the shrinking of the hydroxyl by chemical reaction.4). Put forward two methods to restrict the infiltration: the first is post-treatment (chemical), which is using ammonia and heat treatments make the SiO2 film compact; and the second is pre-filling (physical), which is pre-filling the micro-holes in SiO2 film with some certain washable materials, then clear it out after ZrO2 deposition. To the first way, both ammonia and heat treatments can control infiltration to a certain extent. To the second, naphthalene pre-filling left lots of troubles to solve while polystyrene pre-filling proved to be very well.5). Make a summary to the principles of the interaction between laser and optical film (mechanism, methods to judge damage and the factors cause to damage). Make an expatiation on laser-induced damage testing standards—ISO11254 (how to put laser pulses radiation on films and how to determine a LIDT).6). The monolayer SiO2 and ZrO2 films deposited on K9 glass substrates were prepared with electron beam evaporation method (PVD) and dip-coating method (Sol-gel), respectively. According to porous ratio, thermal absorption, surface morphologies and the coating technics differences of the films, we know that the chemical films have higher porous ratio, lower thermo-absorbtion and lower defects density. These are why the Sol-gels'LIDT were double to the PVDs'. The LIDT of two layer and multi-layer SiO2/ZrO2 have been researched. The laser damage mechanism of sol-gel films may be a laser-induced plasma damage process. They were mostly ablation when damage initiation, and the damage spot expanded drastically with succedent irradiation which proved to be catastrophic. |
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