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23 February 2006 Optical microscopy studies of polymer/liquid-crystal diffractive optics
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Electrically switchable diffraction gratings having periods as small as 5 μm and incorporating nematic LC confined within channels formed in poly(vinyl alcohol) (PVA) films were prepared and characterized. Gratings were produced by first using conventional photolithographic procedures to prepare reusable surface-relief grating molds from a common photoresist (SU-8). An aqueous PVA solution was then drop coated onto the mold and dried, The PVA film was subsequently peeled from the mold and pressed (channel side down) onto an indium tin oxide (ITO) coated glass slide. The channels were then filled with LC using capillary action. Finally, a second ITO-coated slide was pressed onto the backside of the PVA film, forming a polymer/LC grating cell. The diffraction efficiency of each grating was measured as a function of applied electric field strength using 488 nm light. Beam diffraction was greatest in the absence of the field and fell to zero for applied fields of less than 10 V/μm. These studies and atomic force microscopy results showed the LC channels to be ≈ 50-100 nm deep. Multiphoton excited fluorescence microscopy (MPEFM) was used to show the LC was oriented predominantly parallel to the long axis of the channels in the zero field state. Significant nonuniformity observed in the LC orientation was attributed to channel (PVA) wall roughness. Time-resolved MPEFM was used to monitor the LC reorientation process on submicron length scales. The local LC reorientation dynamics were also strongly perturbed by channel wall roughness.
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Aifang Xie, Gregory T. Roman, Christopher T. Culbertson, and Daniel A. Higgins "Optical microscopy studies of polymer/liquid-crystal diffractive optics", Proc. SPIE 6135, Liquid Crystal Materials, Devices, and Applications XI, 613505 (23 February 2006);

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