Fast and Slow Nonlinearities in Epsilon-Near-Zero Materials

摘要

Novel materials, with enhanced light–matter interaction capabilities, play anessential role in achieving the lofty goals of nonlinear optics. Recently,epsilon-near-zero (ENZ) media have emerged as a promising candidate toenable the enhancement of several nonlinear processes including refractiveindex modulation and harmonic generation. Here, the optical nonlinearity ofENZ media is analyzed to clarify the commonalities with other nonlinearmedia and its unique properties. Transparent conducting oxides as the familyof ENZ media with near-zero permittivity in the near-infrared (telecom) bandare focused on. The instantaneous and delayed nonlinearities areinvestigated. By identifying their common origin from the bandnonparabolicity, it is shown that their relative strength is entirely determinedby a ratio of the energy and momentum relaxation (or dephasing) times.Using this framework, ENZ materials are compared against the manypromising nonlinear media that are investigated in literature and show thatwhile ENZ materials do not radically outpace the strength of traditionalmaterials in either the fast or slow nonlinearity, they pack key advantagessuch as an ideal response time, intrinsic slow light enhancement, andbroadband nature in a compact platform making them a valuable tool forultrafast photonics applications for decades to come.