Polyimide (PI) irradiated by pulsed CO2 laser was simulated by finite element method. The finite element model of PI damaged by pulsed CO2 laser was established. We analyzed the temperature and stress characteristics of PI sample under laser irradiation. The effects of laser pulse width and laser spot radius on the damage effect were discussed. The simulation results show that when the stress does not reach the tensile limit,PI will have melt damage,and the body damage is prior to the surface damage. Under the same laser energy irradiation,the thermal stress produced by short pulsed laser is larger than that produced by long pulsed laser,and the effect of thermal stress damage is better. The peak value of stress decreases with the increase of laser spot radius. The larger spot radius is,the worse damage effect is. The occurrence time of peak stress is independent of spot radius.
It has very important application value to investigate the damage mechanism of CaF2 windows irradiated by ultraviolet excimer laser. As significant optical materials, CaF2 windows have been widely used in the ultraviolet photoelectrical field. Because the ultraviolet excimer laser presents favorable characteristics such as short wavelength and high photon energy, the high power excimer lasers are expected to be widely applied in precision laser machining and military field. In this paper, the experiment on damage in CaF2 windows irradiated by 248nm ultraviolet excimer laser was carried out. The damage characteristics of irradiated spots under different experiment conditions were detected by optical microscope. The laser induced damage thresholds of CaF2 windows were calculated by the zero damage probability through linear fitting. The damage mechanism of CaF2 windows were discussed based on the surface characteristics of damage spots. The experimental results indicated that the damage thresholds of zero probability for the 248nm excimer laser to CaF2 windows were 5.6J/cm2 of the incident surface, and 1.1J/cm2 of the exit surface respectively. When CaF2 windows was irradiated by 248nm excimer laser, its damage first occurred to its exit surface, the damage threshold of exit surface was smaller than that of incident surface. As the laser fluence increased gradually, the damage of exit surface was shown to grow exponential and its degree was significantly higher than that of incident surface. This work is helpful to further improve damage resistance of CaF2 windows in high power laser facility. It can provide the necessary references for selection of ultraviolet optical materials and optimization of application.