Berlin 2018 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 29: Focussed Session: Metasurfaces I
HL 29.3: Vortrag
Mittwoch, 14. März 2018, 16:00–16:15, EW 201
Broadband Laguerre-Gaussian Metasurfaces and Direct Phase Mapping — •Alexander Faßbender1, Jiří Babocký2, and Stefan Linden1 — 1Physikalisches Institut, Rheinische Friedrich-Wilhelms Universität Bonn, Nußallee 12, D-53115 Bonn, Germany — 2Institute of Physical Engineering, Brno University of Technology, Technická 2, CZ-616 69 Brno, Czech Republic
We demonstrate metasurfaces based on off-resonant optical scatterers generating Laguerre-Gaussian modes. These modes are characterized by a helical phase profile with radial discontinuities. The metasurfaces are based on gold rods with a length of 220 nm which modify the properties of circular polarized waves. More specifically, the local phase of the scattered light with the opposite helicity can be controlled by the orientation of the rods relative to a reference axis. To accomplish a helical phase gradient, the orientation of the rods placed on a circle around the metasurface center rotates by multiples of π per turn. To achieve radial discontinuities, neighboring rods are shifted by π/2. Since the rods are not required to be driven in resonance, this metasurface allows for a broadband operation in the visible and near-infrared regime. Our interferometric measurements reveal a spiral phase distribution resulting from the introduced helical phase profile. We further present a multifunctional metasurface that coalesces the properties of two conventional optical elements. It generates a doughnut-shaped intensity pattern in combination with the focusing property of a lens. The phase distribution of the beam is measured in two and three dimensions by a holographic microscope and the method of digital holography.