Numerical Simulation Of Long-pulse Laser Damage Mechanism Of The One-dimensional Photonic Crystal Film

Laser is an extremely strong light source. So the laser has been used in many military applications. But this feature can also be a threat to the laser itself and the materials. Although the laser damage ability of thin film materials is very weak, compared to the other laser components or materials, the research on the destruction of the film is later.In this paper, the finite element method is used for the research on the thermal process of the long pulse laser irradiation on one-dimensional photonic crystal film. We simulate the transient temperature and stress field of such crystals during the course of irradiation, then we analyze the damage theory through the stress field distribution of the crystal films. Based on finite element method and heat transfer theory, we create the film model of one-dimensional photonic crystal. Firstly through the one-dimensional photonic crystal structure parameters and the wavelength of the laser we design a film of high reflectivity, which has 9 layers formed by the alternating silicon and silicon dioxide. The axisymmetric model is established. The unitary field strength is calculated by the temperature and standing wave field theory. Each fitted intensity function of the film in the model section is simulated and put on the model. The transient temperature and stress fields are calculated by Ansys. We can see that the temperature shows a ladder down distributing because of different thermal conductivity of the alternating layers, and this cycle of change in temperature gradient caused film stress oscillations up and down, which also can be considered as that the film shows a phenomenon of alternating compressive stress and tensile stress. Because the tensile strength of a film is generally affected by various factors, it is usually damaged by the "push and pull" forces.This thesis can be a reference of one-dimensional photonic crystal laser damage theory, which can also provide a theoretical basis of the laser protection on the optical system and film material.