Sub-picosecond laser damage growth on high reflective coatings for high power applications.

Growth of laser damage on High Reflection (HR) thin film coatings is investigated at the wavelength of 1.030µm in the sub-picosecond regime. An experimental laser damage setup in a pump / probe configuration is used to study the growth behavior of engineered damage sites as well as laser damage sites. Results demonstrate that engineered sites and laser damage sites grow identically which indicates that the growth phenomenon is intrinsic to materials and stack design. In order to analyze the experimental results, we have developed a numerical model to simulate growth. Using FEM simulations, we demonstrate that growth is governed by the evolution of the electric field distribution in the mirror stack under the successive laser shots, which is supported by time-resolved observations of damage growth events. Eventually the results are compared to laser damage observations made on of full scale PETAL mirrors, which fully support the approach.