Quadratisch nichtlineare optische Eigenschaften von metallischen Nanostrukturen auf Lithiumniobat

Die elektromagnetischen Eigenschaften vieler Materialien können durch periodische Strukturierung auf einer Längenskala der Wellenlänge der wechselwirkenden Strahlung gezielt manipuliert werden. In der vorliegenden Arbeit wurde ein Herstellungsverfahren für nanooptische Elemente bestehend aus Gold-Nanozylindern auf Lithiumniobat etabliert. Die spektrale Response eines solchen Elements wurde theoretisch und experimentell ermittelt. Im nahen IR konnten Resonanzeffekte, namentlich lokalisierte Plasmon-Polaritonen untersucht werden. Ein besonderer Schwerpunkt der Arbeit lag auf der experimentellen Untersuchend der Nahfeld-Kopplung mit dem optisch nichtlinearen Substrat und der daraus resultierenden SHG-Response des Systems

Quasicrystal metamaterials: A route to optical isotropy

We introduce a novel class of metamaterials with quasicrystalline meta-atom arrangements and study their properties in comparison with periodic and disordered metamaterials. We show that quasicrystalline metamaterials exhibit isotropic optical propertie

Plasmonic modes of extreme subwavelength nanocavities

We study the physics of a new type of subwavelength nanocavities. They are based on U-shaped metal-insulator-metal waveguides supporting the excitation of surface plasmon polaritons. The waveguides are simultaneously excited from both sides of the U by incident plane waves. Due to their finite length discrete modes emerge within the nanocavity. We show that the excitation symmetry with respect to the cavity ends permits the observation of even and odd modes. Our investigations include near and far field simulations and predict a strong spectral far field response of the comparable small nanoresonators. The strong near field enhancement observed in the cavity at resonance might be suitable to increase the efficiency of nonlinear optical effects, quantum analogies and might facilitate the development of active optical elements, such as active plasmonic elements

Optical metamaterials with quasicrystalline symmetry: Symmetry-induced optical isotropy

We apply the concept of quasicrystals to metamaterials and experimentally demonstrate metasurfaces with isotropic properties and high resonance strength. By comparing quasicrystalline, periodic, and amorphous metasurfaces we quantify the impact of symmet

Optical metamaterials with quasicrystalline symmetry: symmetry-induced optical isotropy

We compare, both experimentally and theoretically, metamaterials with three different symmetries: square lattice, hexagonal lattice, and quasicrystalline Penrose tiling. By relying on an advanced Jones calculus, we link the symmetry properties to the farfield optical response, such as ellipticity and circular dichroism, as the incident angle is varied. We show that hexagonal lattice metamaterials, when compared to the square ones, exhibit less circular dichroism and ellipticity due to their higher symmetry. Furthermore, we show that in contrast to periodic metamaterials, quasicrystalline metamaterials inhibit ellipticity and circular dichroism and open a new route to isotropy in metamaterials at oblique incidence

Polarization phenomena in periodic metasurfaces at oblique incidence

We study experimentally and theoretically oblique incidence polarization phenomena for periodic metasurfaces of different symmetries. We show that the strength of the optical activity, circular dichroism and asymmetric transmission is dependent on the rotational symmetry of the metasurface lattice. We verify the predictions of the analytical model by the experimental study of optical metasurfaces with 4-fold, 6-fold and 5-fold rotational symmetry and demonstrate an excellent agreement

Spatial and spectral light shaping with metamaterials

Plasmonic metamaterials exhibit strong and tunable dispersion, as a result of their pronounced resonances. This dispersion is used to construct an ultrathin light-shaping element that produces different waves at two distinct wavelengths in the near IR range. The optical response of the pixelated element is adjusted by variations in the geometry of the metamaterial's unit cell. Applications requiring spatial and spectral control of light become feasible

Polarization properties of optical metasurfaces of different symmetries

Optical metasurfaces have become a new paradigm for creating flat optical devices. While being typically an order of magnitude thinner than the wavelength of light, metasurfaces allow control of the phase of propagating light waves across the full 2π range and therefore enable the realization of optical elements such as lenses, waveplates, and beam converters. Currently one of the limiting factors of functional metasurfaces is their small range of operational angles. Here we demonstrate both theoretically and experimentally that the angular range can be broadened by increasing the rotational symmetry of metasurfaces. We develop an analytical model based on the discrete dipole approximation that quantitatively describes the response of metasurfaces under oblique excitation. It shows that the effective optical symmetry is doubled for structures with odd rotational symmetry, increasing the angular range correspondingly. We apply and experimentally verify our model for metasurfaces consisting of identical meta-atoms, arranged into square lattices, hexagonal lattices, and on the vertices of a Penrose tiling. The results demonstrate the increasing angular performance with increasing rotational symmetry

Symmetry properties of metamaterials at oblique incidence

We compare, both experimentally and theoretically, metamaterials with three different symmetries: square lattice, hexagonal lattice, and quasicrystalline Penrose tiling. By relying on an advanced Jones calculus, we link the symmetry properties to the far-field optical response, such as ellipticity and circular dichroism, as the incident angle is varied. We show that hexagonal lattice metamaterials, when compared to the square ones, exhibit less circular dichroism and ellipticity due to their higher symmetry. Furthermore, we show that in contrast to periodic metamaterials, quasicrystalline metamaterials inhibit ellipticity and circular dichroism and open a new route to isotropy in metamaterials at oblique incidence