Fabrication and Characterization of Polymer/Liquid Crystal Composite Diffractive Optics by Multiphoton Methods


  • The authors gratefully acknowledge support from the U.S. National Science Foundation (CHE-9709034, DMR-0076169, and CHE-0404578) in these studies.


Direct-write multiphoton photolithography is used to prepare electrically switchable diffraction gratings having spacings as small as 4 μm. Surface-relief gratings are written into poly(methyl methacrylate) films using a sample-scanning confocal microscope and are characterized by using contact-mode atomic force microscopy. The resulting polymeric channels are filled with nematic liquid crystals (LCs) and sandwiched between indium tin oxide-coated coverslips to obtain functional devices. These devices exhibit diffraction efficiencies approaching 30 %. Microscopic LC organization and field-induced reorientation dynamics within these devices are characterized by static and dynamic polarization-dependent multiphoton excited fluorescence microscopy. LCs are found to align predominantly along the channel axis, but exhibit some disorder near the channel walls, resulting from nanometer-scale polymer surface roughness. LC reorientation in response to an electric field is rapid (<1 ms) and uniform, whereas field-free LC relaxation is relatively slow (>20 ms). Both reorientation and relaxation are influenced by orientationally anchored LCs near the channel walls.