Nonlinear optical methacrylate-based filters for optical limiting

The human eye, sensors and photoreceptors can be damaged if they are submitted to laser beams with high intensities and low divergence. In the military field, an optical sensor can be exposed beyond its capacities and be damaged by pulsed laser radiations. In order to have a protection against such threats, passive optical limiting is used1. It is based on nonlinear effects which allow to reduce the intensity of aggressive laser radiations. Nowadays, the development of nonlinear filters for optical limiting is a challenge in order to have protection against threats caused by a pulsed laser beam. As a matter of fact, tactical lasers are a threat toward sensing devices between hundreds of meters and some kilometers.(2,3) This work has for purpose the synthesis of methacrylate-based hybrid polymer systems in order to study their nonlinear properties for the optical limiting in the near infrared part of the electromagnetic spectrum. Several polymers have been selected with specific properties, such as a high transmittance (>80%) over a broad spectrum and a significant third order nonlinear susceptibility chi(3). Poly(methyl methacrylate) (PMMA) is considered as the standard host polymer material because of its high transparency up to 1.6 mu m but also due to its good accessibility. However, to avoid some issues (e.g. exothermy of the polymerization and Tromsdorff-Norish effect during the radical polymerization) regarding the use of methyl methacrylate (MMA) and to improve the nonlinear properties like the nonlinear and damage thresholds, new polymers or hybrid systems have been synthesized. In the present work, a thermoset matrix is studied corresponding to a mix between a reactive oligomer and a monomer both with methacrylate functions. The use of an oligomer and a monomer with a high boiling temperature as precursors allows to prevent the monomer evaporation, resulting in the formation of bubbles in the final material, related to the reaction exotherm.