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30 October 1997 Observation of large anomalous orientational nonlinear response in dye-doped liquid crystals at 1320 nm
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IR z-scan and conoscopic measurements have been performed on dye-doped nematic liquid crystal samples to investigate the influence of the dopant on the orientational nonlinear response of the liquid crystalline material, and the result compared to undyed samples. Both the dye-doped and undyed samples were prepared utilizing a surface treatment which produces homeotropic alignment in the undyed, glass-substrate samples. For samples constructed with non-conducting substrates, the dopant only slightly strengthens the nonlinear response of the host material, and the response in all cases is less than half that observed in samples with ITO- coated substrates. Undyed samples displayed no response at normal incidence for the laser intensities used, regardless of substrate, while doped samples displayed significant self- limiting at all angles of incidence. Increasing the dopant concentration further enhances the observed responses, but the time required to achieve the initial alignment state of the nematic increases more rapidly than the response, and significant delays in response to pulsed inputs are also observed. Laser polarization strongly effects the response characteristics, as expected. Z-scan and conoscopic measurements are used to determine the origin of the unusually large response in the ITO-coated samples Initial efforts with conoscopic techniques have found no evidence of pre-tilt in the director orientation, though more sensitive measurements are in process. The presence of a large nonlinear absorption contribution due to the dopant has been observed, though why only ITO-substrate samples may be affected is still under investigation.
© (1997) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Peter G. LoPresti and Daniel A. Hemphill "Observation of large anomalous orientational nonlinear response in dye-doped liquid crystals at 1320 nm", Proc. SPIE 3143, Liquid Crystals, (30 October 1997);


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