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Fabrication and characterization for visible chiral metamaterials

Authors Gao, Wensheng
Issue Date 2011
Summary Chiral metamaterials are artificial structures that can achieve much stronger optical activities than natural materials. In this thesis I will focus on the fabrication and characteristic of the chiral metamaterials in visible range. I have fabricated chiral samples by multi-step electron beam lithography, electron beam evaporation, and lift off processes. I have also built a home-made polarimeter which can measure the polarization states of incident light, and the transmittance for two circularly polarized light. Three kinds of chiral metamaterials, complementary double layers of 6-fold gammadions, double layer metallic cross gratings, and planar sawtooth metallic gratings, are investigated. The complementary double layers of 6-fold gammadions show significant polarization rotation and circular dichroism; while the planar gammadions obtained by a lift-off from the complementary structures show none of these effects, unveiling the importance between the three dimensional chiral geometry and the optical activity. Furthermore, the circular dichroism is equal for forward and backward incidences, which is reciprocal and follows the Lorentz lemma. The double layer metallic cross gratings show, in addition to optical rotation and circular dichroism, asymmetric transmission for forward and backward incidences, contrary to single layer gratings. The phenomena observed for cross gratings are due to the three dimensional chiral geometry again. The planar sawtooth metallic gratings with different dielectric environment are fabricated. For chiral sawtooth structures with either symmetric or asymmetric dielectric environment, both circular dichroism and asymmetric transmission are observed. For chiral sawtooth structures embedded in symmetric environment, the circular dichroism becomes anti-symmetric for forward and backward incidences. In contrast, achiral sawtooth structures show neither circular dichroism nor asymmetric transmission, independent of the environment. Our experiments provide important results for the chiral metamaterials in the visible range, understanding the mechanism for these phenomena will benefit works, such as negative refraction, optical isolation, optical active modulation, chiral molecular sensing.
Note Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2011
Language English
Format Thesis
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