Optical limiter coatings towards reusable high irradiance shielding

Optical limiters (OLs) are systems designed to protect objects from high intensity irradiance above a set threshold. Often times, these OL systems are in the form of coatings and can be used to protect objects such as sensors, critical components, or human eyes. In this work, we report the successful development of a multilayer reflective OL coating system based on a non-linear Fabry-Perot resonator structure. The structure utilized distributed Bragg reflectors (DBRs) composed of silicon/silicon nitride and a boron nitride non-linear layer embedded in the resonant cavity. The coatings were fabricated via DC and RF magnetron sputtering and exhibited high reflectance (∼99%) over a 525 nm bandwidth with a single resonant transmission peak (∼7%). The optical limiters fabricated in this study exhibited a transmission drop-off when exposed to irradiances above ∼1000 kW/cm² from a 1064 nm Nd:YAG laser, demonstrating an abrupt reduction in resonant transmission. Fabricated optical limiters also demonstrated multi-hit survivability, maintaining low transmittance (<0.4%) after numerous 3.6 ns laser pulse exposures. This multi-hit survivability and high reflectivity offers promising opportunities for improved protection against directed energy weapons. This study lays groundwork for future evaluation of the observed on/off mechanism, as well as further development of high laser damage threshold optical limiting thin films.