Simulation of defect-induced scattering in multilayer coatings

Defects in multilayer coatings significantly increase scattering loss and degrade the performance of the advanced laser systems like gravitational wave detection, laser gyroscope and ultraviolet laser, etc. The quantitative description of the defect-induced scattering in multilayer coatings was rarely addressed. In this work, the scattering characteristics of the nodular defects in Ta2O5/SiO2 multilayer coatings for 1.064 mm wavelength was simulated using finite-difference time-domain method. First, the simulation process was given, several important steps that include structure modeling, far field calculation and far field to angular resolved scattering were presented. The scattering distributions of the nodular defects are similar to Airy diffraction pattern that is from a circular hole. The roughness-induced scattering from the coatings was calculated using first-order perturbation theory. The characteristics of the defect-induced scattering is significantly different from the roughness-induced scattering. The total scattering loss is approximately three orders of magnitude stronger than the roughness-induced scattering.