Theoretical Model for the Spallation of Optical Coating Irradiated by Short Pulsed Laser

Based on the maximum shear stress theory, a theoretical model is developed for the spallation of a plated film under irradiation of a short pulsed laser beam. The formula of the laser energy threshold for the plated film spallation and the relationship between the radius of the spallation zone and the parameters of both the laser beam and the plated film are deduced. As an example, the spallation of a ZrO 2 plated film irradiated by a ns degree short pulsed laser beam is calculated, and both the curve of the spallation radius vs. laser energy and the temperature data are obtained. The theoretical and experimental results are in good accordance with each other, which indicates that the theoretical model is reasonable. The theoretical model with its results declares that the axial rapid thermal expansion, the thermal softening of the film material and the cone shaped shearing sliding induced by both the shearing stress on the lateral cross section and the radial and circumferential stresses are the main causes of the spallation phenomenon.