Suppression effect of the protective film on the defect-induced light field enhancement in optical films

Based on the electromagnetic field theory and finite-difference time-domain algorithm (FDTD), the suppression effects of the protective film on the light field enhancement induced by the metal defect and dielectric defect in the optical thin film are investigated, respectively. Then the refractive index and thickness of the protective layer on defect-induced light field enhancement were analyzed. It was concluded that the peak electric field induced by metal defects decreases with the increasing of the refractive index of the protective layer. For dielectric defects, there exists an optimal refractive index value to achieve the best suppression effect, and the optimal refractive index of the protective layer equals that of the dielectric defect. And regardless of the metal defect and dielectric defect, the thicker the protective layer thickness, the lower the defect-induced light field enhancement and the better the suppression effect. The modeling results help to understand the protective layer mechanism and develop technology to improve the laser-induced damage of optical films.