Laser Thermal Damage Research Of Thin Films Based On Finite Element Method

For a long time, the laser-induced damage has been the bottleneck for the development of high energy laser when high energy laser develops along the higher and more powerful lines. At the same time, laser-induced damage is the main reason which affects the service life of film element using for high energy laser systems. In the laser-induced damage process of optical thin film, some changes occur at the surfaces in the bulk of the components, which presents different damage phenomenon.The important aspect of injury is due to the temperature rise and thermal stress is caused by laser irradiation.In this paper, using the finite element method, the temperature rise and the thermal field inside the thin film components, and the corresponding stress field when the optical film components is being irradiated by laser are analyed. The temperature rise, thermal field and the corresponding stress field of the optical film component when the film element is under laser irradiation are simulated by the ANSYS software. And, the results show the relation profile of the temperature rise of film and the irradiation time, and the heat and the stress distribution nephogram and stress variation along time. Finally, K9 glass substrates and silicon wafers are selected, and then deposit diamond-like carbon (DLC) film on them, afterwards, conduct the related experiments. The simulation results were verified based on the laser-induced damage threshold (LIDT) test, the characteristics of the different damage morpglogy analysis with considering the plating process, film thickness, substrate material and other aspects to verify the simulation results.1. The laser-induced damage is mainly caused by the stress due to the temperature rise and thermal expansion of materials. The three kinds of major injury mode are thermal melt, fracture and stripping. The simulation shows that, when temperature exceeds the melting level of film material, melting damage occurs. Meanwhile, if the melting point of film material is high enough, the thermal stress surpass the tensile strength, it causes the fracture damage. But, when the adhesion between the film and substrate is too small, the delamination damage occurs.2. The laser-induced damage of the optical film components is affected by laser characteristics, materials thermodynamic properties, the thickness, the imprities in the film, etc.Different laser characteristics bring the different damage characteristics.The higher of thin film thermal conductivity, the geater of the damage in the area and depth.When laser heat cannot pass through the film, substrate has no effect of damage.The imparities in thin film is the major cause of damage.3. For the DLC firms, laser-induced damage is mainly caused by the thermal stress.