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Laser induced defect damage on optical thin film

Interaction of laser irradiation with coating defects is studied in this paper. For microdefect, sphere impurity defect model is employed to explain the breakdown process of optical thin film. For sub-microdefect, avalanche ionization by nonlinear absorption is main way to lead thin film breakdown. To testify the effect of defect on the damage of thin film, HfO2 thin films were deposited by the electron-beam evaporation method. The weak absorption and laser induced damage threshold (LIDT) of thin film samples were measured, the damage morphology and defect density of samples were also mapped by Nomarski microscope. These results indicated that the kind of damage morphology of thin film is found to be typically defects initiated. The damage of every sample originates from defects and the damage enlarges from the point of defects. It was also found that the absorption of the films would increase and the LIDT would decrease with the increase of defect density.