Enhanced nonlinear refractive index in epsilon-near-zero materials

Caspani, L. and Kaipurath, R.P.M. and Clerici, M. and Ferrera, M. and Roger, T. and Kim, J. and Kinsey, N. and Pietrzyk, M. and Di Falco, A. and Shalaev, V. M. and Boltasseva, A. and Faccio, D. (2016) Enhanced nonlinear refractive index in epsilon-near-zero materials. Physical Review Letters, 116 (23). 233901. ISSN 1079-7114 (https://doi.org/10.1103/PhysRevLett.116.233901)

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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 ε-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 sixfold increase of the Kerr nonlinear refractive index (n2) 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.