Single-Beam 1-D, 2-D And 3-D Patterning Of Liquid Crystal-Polymer Composites With Spatial Light Modulation Based On Computer-Generated Holography
Zito, Gianluigi (2008) Single-Beam 1-D, 2-D And 3-D Patterning Of Liquid Crystal-Polymer Composites With Spatial Light Modulation Based On Computer-Generated Holography. [Tesi di dottorato] (Inedito)
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The technique of Spatial Light Modulation based on Computer-generated Holography has been successfully exploited to realize patterned samples made by a mixture of liquid crystal and polymeric composites. We believe that the realized structures and, mainly, the employed technique can promote important interests in the development of soft matter photonic devices due to the extreme flexibility and ease of production of our technique, the all joined with the known tuning features of the LC component. Our single-beam technique was developed with three different approaches (Fourier optics-based, direct imaging and interference-based) and allowed the realization of complex structures with micrometric resolution and with accurate control of the writing intensity distribution in the visible range. The irradiance pattern can be, in fact, modified in real time by in-video addressing of the computer-generated holograms (CGHs), without the need for sophisticated mechanical control of the optical table and realignment of the optical elements. Regular patterned samples with good optical contrast were obtained, leading to Photonic Crystals (PhCs) structures with 1D, 2D, and 3D geometries. Regular but not periodic two-dimensional structures were also obtained, leading to Photonic Quasicrystals (PhQCs) of the Penrose, Octagonal, Dodecagonal type and other 2D structures with rotational symmetry up to 23-fold, together with aperiodic structures too like the 2D Thue-Morse pattern. Moreover, samples with structures of defects were also produced with a single-step process. Results of optical and electro-optical characterization of realized samples are presented. Theoretical FDTD studies of the transmission spectra and photonic properties of the structures produced are also shown. The FDTD simulations demonstrate the importance of the choice of the geometric tiling in the building process of the PhQCs, influencing the characteristics of the photonic band-gap of the structures. Moreover, the PBG dependence on the rotational symmetry for low dielectric contrast quasicrystals has been discussed.
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