University of Birmingham > Talks@bham > Metamaterials and Nanophotonics Group Seminars > Nonlinear Optical Metasurfaces: From Enhanced Light-Matter-Interaction to Full Phase Tailoring

Nonlinear Optical Metasurfaces: From Enhanced Light-Matter-Interaction to Full Phase Tailoring

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  • UserProf Thomas Zentgraf (Paderborn University)
  • ClockMonday 14 October 2019, 13:30-14:30
  • HouseAston Webb WG12.

If you have a question about this talk, please contact Dr Miguel Navarro-Cia.

Note unusual time - Room booked from 13:00 to 15:00

For efficient nonlinear processes, the engineering of the nonlinear optical properties of media becomes an important task. The most well-known technique for spatially engineering nonlinear optical properties is the quasi-phase-matching scheme for second-order processes like second harmonic generation. However, the widely used technique of periodic polling of natural crystals only provides a binary state for the nonlinear material polarization, which is equivalent to a discrete phase change of π of the nonlinear polarization. The continuous tailoring of the phase of the nonlinear susceptibility would greatly enhance flexibility in the design and reduce parasitic effects. In this talk, we will discuss nonlinear metamaterials with a continuously controllable phase of the local effective nonlinear polarizability. We will focus on plasmonic metasurfaces with various designs for the meta-atom geometry together with different polarization states of the light. In particular, for circular polarization states, the controllable nonlinearity phase results from the phase accumulation due to the polarization change along the polarization path on the Poincare Sphere (the so-called Pancharatnam-Berry phase) and depends therefore only on the spatial geometry of the metasurface. By using a fixed orientation of the meta-atom, the nonlinear phase can be spatially arbitrarily tailored over the entire range from 0 to 2π. In contrast to the quasi-phase-matching scheme, the continuous phase engineering of the effective nonlinear polarizability enables complete control of the propagation of harmonic generation signals, and therefore, it seamlessly combines the generation and manipulation of the harmonic waves for highly compact nonlinear nanophotonic devices.

We will discuss the concepts of enhancing nonlinear processes with simultaneous phase engineering for the manipulation of second- and third-harmonic generation from metasurfaces and the restrictions with respect to symmetry and geometry of meta-atoms. As an example for novel applications based on nonlinear metasurfaces, we will discuss in detail the properties of a nonlinear metalens and generalize the lens equations to include nonlinear processes.

This talk is part of the Metamaterials and Nanophotonics Group Seminars series.

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