Enhanced nonlinear refractive index in epsilon-near-zero materials
  New propagation regimes for light arise from the ability to tune the dielectric permittivity to extremely low values. Here we demonstrate a universal approach based on the low linear permittivity values attained in the epsilon-near-zero (ENZ) regime for enhancing the nonlinear refractive index, which enables remarkable light-induced changes of the material properties. Experiments performed on Al-doped ZnO (AZO) thin films show a six-fold increase of the Kerr nonlinear refractive index ($n_2$) at the ENZ wavelength, located in the 1300 nm region. This in turn leads to ultrafast light-induced refractive index changes of the order of unity, thus representing a new paradigm for nonlinear optics. 
L. Caspani, R. P. M. Kaipurath, M. Clerici, M. Ferrera, T. Roger, M.   Pietrzyk, A. Di Falco, J. Kim, N. Kinsey, V. M. Shala...
physics.optics