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POLIPHEM - New type of nanoscale polymer-LC switchable photonic devices

: Sakhno, O.; Slussarenko, S.; Stumpe, J.


Meerholz, K.:
Organic Holographic Materials and Applications II : Denver, Thursday 05 August 2004
Bellingham, WA: SPIE, 2004 (Proceedings of SPIE 5521)
ISBN: 0-8194-5459-1
Conference "Organic Holographic Materials and Applications" <2005, Denver>
Conference Paper
Fraunhofer IAP ()

A new type of volume holographic gratings based on polymer-liquid crystal composite named POLIPHEM (POlymer Liquid Crystal Polymer Holograms Electrically Manageable) is presented. The new composite material in combination with the proper holographic fabrication results in switchable holographic gratings with high diffractive and electro-optical parameters. Periodic structures consisting of alternating polymeric and LC-rich regions with aligned mono-domain morphology of the LC are formed due to photopolymerisation and phase separation of the initially homogenous film of photo-curable monomers and liquid crystals under illumination with an interference field (rec=364 nm) at room temperature. Compared to typical holographic polymer-dispersed liquid crystals (H-PDLCs) POLIPHEM films are characterized by the absence of light-scattering, strong anisotropy after holographic exposure, low driving voltages and fast electro-optic time-response. The kinetics of the holographic rec ording under different irradiation intensities were investigated at test= 632.8 nm, the microstructure and the electro-optical response of POLIPHEM transmission gratings have been analyzed. POLIPHEMs were realized in the pitch range of 0.28-6 m. The diffraction efficiency of more than 96% was achieved for p-polarized probe light (for test=632.8 nm). Possible mechanism of POLIPHEM formation is discussed briefly.