For instance, the ENZ crossing point of ITO changes depends on annealing temperatures. In general the onset of the nonlinearity will depend on how close to zero the linear dielectric constant can be designed, via doping, material processing, or a combination of both. In practical terms, the nonlinear optical properties of an ENZ material can in principle become very large and dominate linear optical properties even at what may be considered moderate intensities, or a few megawatts per centimeter squared (MW/cm^2). Like the ITO, the ZnO had an ultrafast nonlinear index change close to unity. The work on ITO was quickly followed by another measurement on a transparent semiconductor similar to ITO, Al doped ZnO. Until now, typical changes in the index of refraction for ultrafast nonlinear materials were <1%. The experimentally observed change in the real part of index of refraction near the ENZ frequency of Indium Tin Oxide (ITO) was measured to be 0.7 or 170% of the linear index and had a response time on the order of a few hundred femtoseconds. Therefore, the change in refractive index becomes large as the permittivity becomes small, suggesting that the ENZ frequencies of a material system should give rise to strong nonlinear optical properties. In particular, it was noted that for a given change in the permittivity, the resulting change in the refractive index for a lossless material is related to the inverse square root of the dielectric constant. Recent research on nonlinear Epsilon Near Zero, ENZ, materials have demonstrated that these materials have the potential to overcome these problems to finally bring efficient optical limiters to fruition.Ī recent experimental result on the nonlinear optical response of an ENZ material showed not just a large nonlinearity, but an unprecedented nonlinear response which could have implications for many nonlinear devices. Slow nonlinear devices can have large nonlinearities but these are not usefully because several optical pulses are needed before the limiting process engages. Progress in this area has been hampered by the ultrafast materials available which until recently had very small nonlinear coefficient. OBJECTIVE: The objective of this task is to investigate the novel interaction of electromagnetic radiation with materials that have the dielectric constant close to zero, with the specific aim to understand and thereby enhance the nonlinear interactions for applications in optical limiting for sensor protection.ĭESCRIPTION: A long standing application of nonlinear optics is that of optical limiting for sensor protection.