Third-Order Optical Nonlinearities in Antireflection Coatings: Model, Simulation, and Design

Antireflection coatings are used in many optical systems for improving their optical performance. Thereby, the target is the suppression of unwanted reflections and/or the increase of the transmittance. In both cases the resulting solutions are identical when no optical losses are relevant. Typically, a proper selection of materials and deposition technique will result in neglectable losses in most applications, and distinguishing between both aims is not necessary. In the case of high energy laser optics, nonlinear optical effects often become relevant and may result in significant changes of the optical performance. In particular, two-photon absorption may provide an additional loss mechanism, which is absent in the linear case. We will present a practical numerical model for calculating transmittance and reflectance of multilayer coatings taking third-order optical nonlinearities into account. Thereby, the impact of different discretization of the complex refractive index profile to the predicted system performance will be investigated. Additionally, aspects for parallelism of the calculations will be discussed. The developed method will be applied for the design of different antireflective coatings matching various types of targets.