Optical limiter based on epsilon-near-zero materials

The emerging class of epsilon-near-zero (ENZ) materials are promising candidates for non-linear optical (NLO) applications like optical limiting. In ENZ materials, large NLO effects, particularly in the infrared, have been demonstrated at much lower optical fluxes than have been shown in traditional NLO materials. The effect has been linked to the unique electric field concentration that occurs in ENZ materials near their zero permittivity frequency. In addition to producing extraordinary NLO effects, many groups have demonstrated that the property change is an ultrafast (fs) phenomena. These shared properties, ultrafast response and low threshold for NLO change, lend themselves to use in optical limiting applications, where ultrashort pulsed lasers are becoming an evermore concerning threat. During a recent Phase 1 feasibility study, Third Floor Materials demonstrated that the NLO effect in ENZ materials designed to operate in the MWIR, could be effectively leveraged by combining them with optical antenna structures. The antenna structure allows coupling to the ENZ mode from free-space and concentrates electric field intensity within the ENZ material further augmenting the NLO effect. Some of these hybrid meta-material/ENZ structures showed better than 2 orders of magnitude limiting at a 3 µm wavelength. To extend the usefulness of the hybrid antenna/ENZ approach, Third Floor Materials will pursue two principle objectives in the Phase 2 follow on program; an effort to broaden the response of the ENZ limiting structure across the entire MWIR (3-5 µm) and a parallel thrust designed to increase ‘off-state’ transmission. Similar to the Phase 1 study, our team will use real, measured ENZ material properties to develop a NLO FDTD model of an ENZ limiting system – and build a prototype for Army AvMC evaluation. We believe that the proposed approach will significantly expand Army understanding of ENZ materials and providing a compelling early use case in the form of an ultra-fast optical limiting solution.