Impact of high refractive coating material on the nodular-induced electric field enhancement for near infrared multilayer mirrors.

Electric field enhancement due to nodular defects within quarter-wave optical thickness multilayer mirrors is impacted by the inclusion diameter, inclusion depth, inclusion composition, nodular shape, multilayer angular bandwidth, multilayer coating materials, number of layers, angle of incidence, and polarization. In this modeling study, the electric field enhancement for surface inclusions with diameters up to 2 µm irradiated at 1064 nm at either normal or 45 deg incidence is calculated for high refractive index materials over a refractive index range of 1.7-2.3 for oxide materials commonly used in the near infrared. The thicknesses of the multilayer mirror thin films are determined for each high refractive index material by a requirement to meet a 99.5% reflection. The refractive index was found to have a significant impact on the electric field enhancement, which may offer some insight into the optimal material choice to produce high laser damage threshold mirrors.