Recent surprises in nonlocal and nonlinear photonics

Abstract: In this talk, we will discuss two recent observations from our group that have challenged widespread assumptions held (by us included!) about the optical response of commonly used optical materials: that material polarization can safely be considered to respond locally to the electric field and that the second-order nonlinear response of amorphous films should vanish due to centrosymmetry. In the first part of the talk, we will describe our proposal for a new type of optical antenna dubbed a “photonic gap antenna”, and our realization of its extreme version using an epsilon-near-zero (ENZ) material. Such antennas can provide electric field enhancements of >100 and large Purcell factors without requiring stringent nanofabrication. To our surprise, when measuring third harmonic generation as a proxy for field enhancement, sharp peaks emerge in the response that are completely absent in our full wave electromagnetic calculations. We find that the appearance of these peaks can only be explained when including nonlocality in the dielectric response of the ENZ material. Nonlocal simulations show that the volume averaged field enhancement can be 4–6 greater than that predicted by the local model, which becomes an important consideration when designing optical devices. In the second part of the talk, we will describe our recent discovery that amorphous thermally evaporated organic thin films of small molecules can have second-order optical nonlinearities on par with those of state-of-the-art nonlinear materials (c(2)31, c(2)33 >50 pm/V), with the important advantage that they can be deposited on arbitrary photonic platforms. We will show that by harnessing the interplay between dipole-dipole interactions and surface energy minimization, it is possible to spontaneously break centrosymmetry during thermal evaporation, without the need for special alignment procedures. In addition to its applications in photonics, this observation has allowed us to better understand molecular alignment beyond the mean molecular orientation angle. . Co-sponsored by: Prof. Nicolas Quesada Speaker(s): Stéphane Kéna-Cohen J. Armand Bombardier J-1035, Polytechnique Montréal, Montréal, Quebec, Canada, H3T 1J4