Large nonlinear phase shift in Epsilon-near-zero materials: the effect of group and phase velocity

Sepehr A. Benis; Natalia Munera; Eric W. Van Stryland; David J. Hagan

doi:10.1117/12.2569291

20 August 2020 Large nonlinear phase shift in Epsilon-near-zero materials: the effect of group and phase velocity

Sepehr A. Benis, Natalia Munera, Eric W. Van Stryland, David J. Hagan

Proceedings Volume 11460, Metamaterials, Metadevices, and Metasystems 2020; 1146010 (2020) https://doi.org/10.1117/12.2569291
Event: SPIE Nanoscience + Engineering, 2020, Online Only

Abstract

Materials with vanishing real part of permittivity, also known as epsilon-near-zero (ENZ), have emerged as a new paradigm to obtain large optical nonlinearities. Transparent conducting oxides such as indium tin oxide (ITO) naturally exhibit an ENZ condition in the near-infrared and close to their plasma frequency. The peculiarity of ENZ materials is their highly dispersive nature explained by Drude model, allowing to obtain reduced group velocity at frequencies where the phase velocity is enhanced. This condition can dramatically increase the phase sensitivity caused by any given changes in material permittivity. To accurately address the NLO mechanism in such materials, we present a generalized formalism for the nonlinear phase shift for a dispersive material, where it includes contributions from both group velocity and phase velocity. We experimentally demonstrate that the nonlinear phase can reach to the values close to π/2 when the probe beam is at ENZ, while the index change in the conventional definition is not enhanced necessarily. In this work, we present nonlinear optical measurements using the nondegenerate Beam Deflection (BD) methodology at normal incident together with cross-phase modulation experiments. BD is a pump-probe method that directly characterizes the ultrafast response of the nonlinear phase-shift, hence nonlinear refraction. We see no polarization dependence proving that bound electronic third-order nonlinearities are negligible compared to the sub-picosecond fast carrier effects. We also present that frequency shift is highly sensitive to the temporal dynamics of the nonlinear phase shift suggesting that short pulses may help to improve the magnitude of frequency shift.

Conference Presentation

Citation Download Citation

Sepehr A. Benis, Natalia Munera, Eric W. Van Stryland, and David J. Hagan "Large nonlinear phase shift in Epsilon-near-zero materials: the effect of group and phase velocity", Proc. SPIE 11460, Metamaterials, Metadevices, and Metasystems 2020, 1146010 (20 August 2020); https://doi.org/10.1117/12.2569291

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